Hmm... Generally, the way your follow list gets nuked is by following someone from a client that is not your usual client, and which hasn't loaded your follow list. Therefore, it creates a new one and broadcasts it out to your relays, overwriting your existing follow list.

You can check and see if you can restore a previous follow list by going to https://hist.nostr.land/ or https://metadata.nostr.com/. I think the second one only works if you have actively gone to it and backed up your profile previously, though.