404 errors on all pages “Sorry, … no posts matched”

After two months in development, and for now apparent reason, my page structure seems to have collapsed. I’m hoping you can help.

My permalink structure was set to /%category%/%postname%/
Everything was working fine.

I did not change the permalink structure until after the errors starting occurring (at which point I attempted to regenerate).

For seemingly no reason, ALL of my pages started returning 404 errors. OK, so here are the steps I took:

1. Change the Permalink structure back to default and reset (not fixed).
2. Delete .htaccess, change the Permalink structure back to default and reset (not fixed).
2. Delete .htaccess, change the Permalink structure back to default and reset. Set .htaccess permissions to 666. (Not fixed!)

Right now, I have an active .htaccess with default permalinks.
Some of my pages are pointing to my web host’s 404 page (see: https://americannoise.com/american-noise-terms-of-use/ ) while SOME of my pages are returning “Sorry, no posts matched your criteria.” (See: https://americannoise.com/?page_id=2)

I don’t see any pattern between the two–further, I don’t know why SOME of those would kick back to my server’s 404 page, not my own. Weirder still is that SOME of my pages still work! For example, this page works fine: https://americannoise.com/?page_id=25

I have no idea what to do here. It’s a big problem, obviously.
Thanks for your help.