The permalinks for my Wordpress sites quit working for no reason that I can figure out. I have 4 Wordpress sites and the permalinks for all 4 sites quit working at the same time - Sunday evening. When I clicked on a post link, I got a 404 error message. I checked all 4 sites and I had the same problem at all 4 sites.
I was able to fix the problem by switching the permalink settings back and forth. I use the day-name custom permalinks. I switched to the Wordpress default permalinks and the post links worked. After that, I switched back to the custom day-name permalinks and they worked again.
This was quite a scare for me. I had made some format changes on index.php on two of the sites on Sunday afternoon, but I didn't touch the other two sites.
I called my host and they denied any involvement. Does anyone have an idea about what may have caused this?