After Ben pointed out that there’s weird issues when starting from the menu I tried it out and had the same. I followed his instructions, removing collision from tank body, tracks, turret and barrel, then adding box collision on the tank body. Now I get weird jittering for the AI tanks and the projectiles don’t collide with tanks either. I tried moving the tanks above the ground, so they definitely aren’t overlapping when the level starts, but that didn’t really help.
Collision works fine when I start from the Battleground map, though.