While I was typing in the search window of the 3D Warehouse, suddenly my model started showing dashed lines through all the walls and I can’t figure out exactly what to name this problem or how to fix it. Still very much a beginner. This is the first problem where I couldn’t find the solution by googling.

This is the problem I’m talking about:

I apologize if this is a silly obvious thing - but I’ve hit a wall with this one. Is this Hidden Geometry? I use the web-based free 2019 Sketchup.