I just finished replaying the mission Gustav Line, and I think my tanks have some kind of issue. I'm pretty sure one of my units lost 4 tanks in seconds fighting a (already engaged) dug in infantry. A similar thing happened later in the mission with another tank unit.

I don't remember tanks being this weak in my first playthrough so I saved the replay, if there's any way I can get it to you I would like to know.

This also seems to have happened in Battle of Leonforte. although I didn't save that replay.