Geometric (?) glitch

I make cc by mashing different meshes together (frankenmeshing I believe it’s called) and sometimes it glitches out in the auto generated thumbnail and gallery pic (it works fine in my cas). I also share my cc and some people find it glitches out IN game. I wanted to add a photo but I had a really hard time doing so, so I’ll try my best to explain the glitch. It’s currently happening with the pants part of a full body cc and the legs are invisible and there’s these crazy lines and boxes sticking out from all angles, some are the colours of the broken mesh and some are this light blue colour that I didn’t use at all on the piece. Does anyone know what’s happening here? For this piece in particular I already completely replaced the pants’ mesh and it’s STILL happening?!?