Permalinks keep reverting to 404 unless I re-save them

I’m running the latest (and constantly updated) version of WordPress on Nginx.

Every now and then I wake up to a site full of 404 errors. The fix is to go into the permalinks and just save the settings on that page. This typically fixes the issue for a day or so.

This was happening to another site of mine on the same server. It suddenly stopped being an issue. My point here is that not only do I not know what’s causing it, but I can’t even tell what’s fixing it.

Same problem for the last few weeks, using nginx not apache,
Switching rule saving, then switching rule back and saving fixes it for a day…