I couldn't reproduce your issue, but I've reuploaded all container trucks to fix another minor bug I've found, so I changed the base as well. Update your assets manually and you shouldn't have this problem anymore.

The container truck (trailer). The rectangles are visible only when there is a container (or two containers) on them. I can only find the trailer with no container using Advance Vehicle Options and they are totally normal when carrying nothing or the fluid storage tanks.

Which one do you have issues with?

Still exists after re-subscribing. I think at this point I'll just prevent them from spawning 🙃

Check if you have up to date version of the vehicles (Steam doesnt seem to update assets automaticaly, so you ned to unsubsrcibe, open the game and resubsrcibe) and if you dont have any mods messing with alpha textures. Those pink rectangles are there to help me allign submeshes (e.g. cargo) on trucks or trailers, and they should be invisible. I couldn't reproduce this issue in my game.

Notice that some trailer tires come with a spinning rectangle attached to them when viewing from the back