I'm seeing a lot of follow list questions on asknostr amd elsewhere today, so i thought I'd share a blanket answer:
Every time you follow or unfollow someone, a new version of your follow list is created, meant to replace the old one. Some relays may not get the memo because there's lots of relays.
When you sign into a new client, it asks whatever relays it connects with, for your follow list. The relays send what they have, which may not be the current version. If you follow/unfollow from the new client, it triggers the follow list update, editing whatever copy of your list that it has, which is then broadcast to many relays. That's how you lose some of your follows.
If the relay being asked doesn't have a copy of your list, it says "this user doesn't have one" and the client creates a new, empty list. Again, the follow/unfollow action triggers publishing & that is how you lose your whole follow list.
In short, it's a client issue because it's not making requests about you to the relays that you have in your "write" relays list, but instead to some other relay(s) that you've never sent data to before or that have old data. Avoiding the follow/unfollow actions when trying out new clients will mostly mitigate the problem. If you start using that new client regularly, eventually your follow list will make it to the appropriate relays and/or the client will get updated and start making requests to the appropriate relays.
Visit metadata.nostr.com or follows.nostr.com on occassion to back up your follow list. You can then rebroadcast the correct version, if you experience this unintended follow list fiasco. Alternatively, you can add wss://hist.nostr.land to your write/outbox relays. It will keep the latest previous version of your follow list. You can then visit the homepage to restore.
Some clients offer in-app follow list restoration, both as a paid and free feature, as well.
