Tried that. This time with selecting a file from local storage. Same thing.
What error do you get in your browser's console?
!
This time it worked again. There's a lot of error spamming going on my Waterfox console, I'll just post the latest one, which is in there about a million times. Fail on getting domain pref: NS_ERROR_HOST_IS_IP_ADDRESS: Component returned failure code: 0x804b0051 (NS_ERROR_HOST_IS_IP_ADDRESS) [nsICookieBannerService.getDomainPref] receiveMessage resource://gre/actors/CookieBannerParent.sys.mjs:182 CookieBannerParent.sys.mjs:197:19
Talk to you in a little bit.
Try to log out and back in. Server thinks you are not logged when sending that [POST] request.
Must be a corrupt session cookie.