Is there a hidden mechanic for movement reduction from weapons weight?

It seems when a soldier has above 10 summary weight in ready slots you lose some movement speed (overall weight IS within the limit or even under it).
But it’s kind of inconsistent - sometimes I get move reduction, sometimes I don’t. Can’t know for sure until I’m in combat.
Is this unexplained feature or bug? If feature, how exactly it works?

I just go by the little line under the soldier. When it goes red I remove something.

No, that’s normal over-weight. I’m talking about situation when I have reduced movement, below what I should have from armor alone AND despite staying within total weight limit.

You mean like a itemised of all your gear?

Experimented a bit more with it. Seems there is just a bug with equipment weight at mission start. Ready slots weight wasn’t what was causing it.

2 cases of same loadout (anu assault legs, golem body, eidolon helm + gauss heavy + synedrion sniper), with only one difference: 15/16 weight vs 16/16 (extra sniper clip).
16/16 works as it’s supposed to.
15/16 get -1 extra movement. If I drop anything and pickup during mission I get correct max movement.