Love the game, looking to help make it better. I was raiding my first enemy base and came across my first game breaker. What happened right before might also be instructive as to the source of the issue. I had one of my 2 support characters attacked by a pincer, I hit it with the mechanical arm shock (killing it) then repaired the damage on himself.
My second support soldier had the exact same thing happen and I went to execute his electrocution melee attack. However, because I had just done so I double tapped the attack button before the camera had finished swinging around to view the target. The result was my UI dissapearing and the two characters lining up in front of one another in their ‘combat bounce’ stances to be forever locked in a staring contest of epic proportions. (Their animations never fired nor did the mechanical attack.) I let it sit for 15 minutes because I was reticent to lose the progress then alt+f4’ed my way back to the desktop.
Sometimes I wonder in situations like this whether they stay that way when I close the game, forever stalled, forever unfulfilled. Anyways, I’m one of the idiots still using Windows 8.1 64 bit if that’s relevant. My graphics card is an Nvidia GTX 1070 and my processor is an intel i5. I also have 16gb of ram. Let me know if any other information would be relevant or if there’s a place to get a crash dump when there wasn’t technically a crash.
Keep up the good work heroes, we’re all counting on you. 
Edit Note: This is actually a bug that I ran into on the recent XCOM games too, it was extremely unreliable to hit the fire button before the camera had finished aligning. If memory serves the team for PP shares some talent, so it may help narrow things down to look at any similar attack animation/camera control code.