Happened a few times. I think it's a syncronization/stale event thing. I've seen warnings on Primal to effect that commiting to a follow might lose data (so don't if you see that.)

It is handy to put a relay on a local node or vps to backup all your events, sth like Start9/Umbrel or on a vps. If anything happens can rebroadcast events from other relays back to yours. I used https://usenostr.org/relay (uses same frontend as Umbrel) then broadcast with https://github.com/leesalminen/nostr-broadcast can use a tool like https://github.com/rot13maxi/key-convertr to convert my npub/nsec from decimal to hex.

Bit of a rabbithole, but worked well!