Alright thanks I'll try one of those. It's just a bummer. I try to make the model clean and remove all the useless junk and that happens. It can be a big bummer.

I'd rather show you what is happening than try to describe it. See video.
https://youtu.be/D6PdoW099kg
I include the model file. I'm just wondering what is going on. Maybe how to prevent it from happening. It doesn't happen on every model, but it does happen. And it's a bummer.

556rifleshort.skp