Especially (but not limited to) on random maps it feels like often crabsman are spawning or coming from already really cleared and been through areas. Is this some improbability engine to make game harder, bug or for other reason intended behavior?
Queen should have unexpected or less expected spawn location, but this kind of mechanics seems quite unrealistic, even it raises difficulty.
I’m not sure if they spawn there after you searched the area.
I think they are there whole the time, but for some reason your soldiers don’t spot them. Looks like the system has too low frequency of making spot checks. While your soldiers move they sometimes omit enemies who are at soldiers’ sides. We can compare it to you sitting in a fast moving bus looking through the window. If bus is moving too quickly then you can’t spot everything that the bus is passing by.
While I often have to do a full sweep to find the last crab, I’ve never had the case where I could be positive I checked everything thoroughly enough and he just spawned there. As far as I’m aware, aside from the Queen and her escort, all crabs are present on turn 1 and don’t spawn later on.
If I were wrong, I’d agree with you though. Enemies shouldn’t appear out of nowhere without justification (advanced aliens that can teleport, infiltrate, tunnel or anything else are fair game)
This mighttbe also an explanation, but would be bug as well.
Let me give you a clear example.
You see a crabman (or two, or tree …). You kill him/them and progress a bit in the direction where they were and ahead to check area. Its clear. You start turning to next direction and voila crabman or two pops exactly where battle was / you were previous turn. They could not magically appear (unless teleported) and they get quite advancing position caughting you often facing them back and not in cover.
This does not happen every time, but is stressful. I am OK with more of their reinforcements coming from outside but almost next to you? And its not like there were some nearby covers they could hide, this happens on tunnel like one direction or open square spaces.
Interesting. Didn’t happen to me yet. But if something like that happens then it is really not ok.
A similar situation happened to me, a carbman has pop just behind my soldiers in the start corner of the map, after 2 or 3 turns of game.
See, the enemy is adapting already! Introducing the invisible Crabman Ninjas 
I know that enemies spawn over the course of the battle. I’ve seen crabbies spawn alongside the queen. I can’t be sure if they spawn anywhere else, but it would seem more probably that you get “odd spawns” on the “random maps” than on the included scenario, since they’re probably not scripted with the same detail. I don’t know whether or not monsters are supposed to spawn like this in the final game, but according to the Game Guide, the queen will eventually have an ability to spawn minions, and everything currently implemented could definitely be subject to change before release.
Are you sure that the monsters spawned in a location you’d already been or just moved to there? As far as I understand, aliens still move on their turn even if you haven’t spotted them.
Yes. Since that are contained no place they could hide and was kind of scouted. I am versed in game mechanics and would expect them to come from some place, that is why “already explored” is included.
I could guess it could be just bad random spawning.
No, currently queen spawns no enemies, that would be logical but limited to queens surroundings and area and could advance as much as one can per turn.
Or as @kompan said, its an adaptation method / old new way of punishing for early success
Take a look at Urisnus battle for hangar since 15:00
Also an other players comment on video
Barry Hatchel
5 days ago
Don’t think it’s a teleportation bug. I think the map generates random grunts. The ones session I got in with this build, I would clear an area and have foes stepping out from behind rocks I know I’d cleared.
Now I understand what are you talking about. This is not a bug. It is a feature. Enemies just spawn on the edge of the map, 2 or 3 tiles from actual map’s edge. You can treat it as they came from close vicinity of the map attracted by the fight, just like the queen is doing. Thus you need to remember not to stay in the open when there is no wall covering you from that edge of the map. There, up to 3 enemies, can show up and you are screwed. Until now I was thinking that you all talked about enemies showing out of nowhere in the middle of the map.
“Pouring from edges of map” not really coming as movement? That is not a feature.
I hope this will be changed, my belief is that XCom enemies do not spawn, they move like your squad. A bit of tolerance could be added to some boss spawning skill or reinforcement, this way it is … game-breaking in negative way as Urisnus experience illustrates even better … Such a dramatic battle just for few squares of enterance.
Hope this will be “fixed” even its all pre-pre …
I’ve lost quite a few soldiers to enemies spawning from areas I had previously (and thoroughly) cleared 2 or 3 turns ago.
And I like this feature, it makes you move toward center and defend there, instead of hiding in the corner of the map. 
So map design changes how you need to behave.
It can be seen as “anti-camping” measure, but is artificial tension maker and too unrealistic.
If it was arcade shooter, I wouldn’t really mind it.
Unrealistic is that enemies come from outside of the map?
And what if you could get reinforcements in this way? Let say that enemy has launched surprise attack at your base. Base defence mission is triggered and map is generating battle at the base entrance. You can quickly send only 6 soldiers, and the rest will come later. So during the battle you try to hold the line with those 6 soldiers and then you get additional ones coming from other base sections, so from different directions. I would say that having such reinforcements would be nice. But it would be unrealistic if they would spawn in the center of the map. And it is quite realistic that they will spawn on the edge of the map, where it has border with those other sections of the base like living quarters and research facilities.
Thus enemies also should have this opportunity to receive reinforcements. Just like arrival of the queen, but from more random directions in random set of turns.
I can agree this is little bit annoying but still nice addition to the tense and game mechanics. Having only those enemies who were generated on the map could be less fun and sometimes map would be a little bit overcrowded. And in this way you have fight with nice number of enemies which is stretched in time.
And there can be some research tech used little bit later in the game allowing you to use some radars or satellites to give you the number of enemies approaching and from which directions. 
Yes, because there is no such thing as “outside of map” in Xcom series.
In fact, thing that they are basically “warping” or spilling over from Area X (outside of map is new dimension) is disturbing. It kills the game realism, which is facing the enemies as they are + countering their actions. Their strength is in AI, not in random warping of 2-3 enemies at once - we are a bit back to EW style, and a bit backward as warping is even worse then alien pods (discovering small groups).
In XCom mechanics they could start from some location, like those who come with queen and then walk from there.
I wouldn’t consider it unrealistic that enemies are drawn to an area by the noise of gunshots.
Whether it’s a good game mechanic or not is a different matter.
I’ve experienced this mechanic being used in Dead State, it made sense within that game world as the whole mythology of fighting zombies revolves around trying to do so quietly. I think I’d want to see PP in its entirety before deciding whether the same mechanic fitted in here.
But Phoenix Point can introduce it to XCOM series. Something new which won’t ruin gameplay is always welcomed. 
Of course i think that the map with enemies spawning around you is the most difficult right now. In last game I had 16 enemies there overall and 9 (6 grenadiers, 1 gunner, 2 tanks) of them spawned just before or right after the queen. Without Armadillo it would be a nightmare. When Snapshot will ballance things it can be quite interesting.
It can ruin the gameplay too. I am not against NEW feats. build upon the old. Sid (Meier) had some 30% new - 30% similar - 30% new formula, but as time goes on new feats were more ruining the game (CIv series) and making it less looking like part of same game. In the end Civ3 had more civs, wonders and better conquests then Civ5.
I do find it as artificial hardening of the game, even it can be seen as challenging at times (which is good)
I really dont know is current warping situations bug or feature, content holder until next BB or “final end game solution”?
Sidenote: @UnstableVoltage has left instructions have to report bugs which is nice and requires detailed answers. Nice guide Lords gift! (Bozidar is the name of the bugfixing team leader).
That would be nice touch of something XCom style to do. But “our gunfire” does not make enemies near to come to battle by playing their turns in movement and shooting, but warps them nearby.
That is a big, big difference in gameplay. Thus we should warp too >:)
I do consider warping with the queen as normal part of the battle. But those “bad random spawns” I do list as serious bugs. Alien start positions (beside a queen and its minions) should be scripted as start position, AI is in the way they play, not in the way they spawn.
With such spawning ability we could beat as many queens as desired.
If they were animated and were running from outside of map instead of “warping” would you consider it a feature not bug? For me it is not big difference if queen comes with 2 minions or with 9 minions. Even if they spawn little bit earlier. 
There are only 7 enemies at the beginning of the map