If you make a change to your follow list using a new app that doesn’t back up your list as a safeguard, it might overwrite your follow list with a blank version.
Also, you have a large follow list (over 1500) that may be fragmented across relays. Certain relays limit by default the amount of data that can be signed in a single event and silently fail when publishing, so you might see different counts in different clients. This has caused me a lot of problems. NIP-46 signers also tend to choke on large follow counts.
