Sync won't sync, and repeatedly asks for password and 2FA

Firefox sync is synchronizing; most notably, my passwords are not available. I am repeatedly asked to sign in; even after successfully signing in, I am immediately prompted again for my password and 2FA. After logging in (even if prompted to do so again) Firefox reports that it is syncing correctly, but password auto-fills are unavailable, and about:logins shows no entries, as is this were a fresh install. On restarting Firefox, I am once again logged out of Sync and need to log in yet again. This is not affecting my mobile device; only my desktops and laptop. I first noticed the problem about two days ago. Since then, I have tried the following suggested fixes, to no avail: * Restarting Firefox * Restarting my computers * Restarting in safe mode * Creating a new profile * Resetting my password * Logging out of all devices and logging back in I would welcome suggestions on how else I might address this. Thanks, Kestrel