It has been happening quite for some while for now, but it has happened even with no mods on the combined arms showcase (the one with the IFV and the infantry on Altis).

The AI out of nowhere will get away from their group making themselves single units. This in the mission will have the effect that "we had too many casualities" and it will send me into an autolose state. If not on that mission, it happends when the AI gets hit or when i switch control of the units, the AI just assumes that they dont have to be part of their squad anymore and leave. It is quite annoying.