Previously functional, unedited files now have incompatible geometry

I’ve been trying to add a new model to one of my projects and it has 8 self-intersecting faces. I’ve re-opened the old model files I used and they’re encountering the same issue, and none of these have ever been edited by me. When I delete the problem faces, it then says I don’t have a “solid body in the model,” despite there very visibly being one. Anyone else have these issues, and know how to fix them?

Those eight black dots are the problem faces. Mind, this model should only be one face, and loaded in as only one face in my previous trials.

Hello guyer2023
do you have a link to your project so that we can have a look at it?

Best regards Sebastian