Permalinks keep breaking

So I set up my permalinks using the category/postname structure, and they work great.

However, they keep breaking sporadically. All of a sudden, the category links won’t work, leading to a “you do not have permission to access this page error”

I can instantly fix the problem by going to the permalinks settings and clicking “Save” again. Then they work again, but will break — seemingly for no reason — later on.

Has anyone else experienced this problem and/or found a fix? Is there some file that is being refreshed that causes the links to break?

Thanks so much.