Iris.to and nostros have been reported to wipeout your following list.

https://github.com/KoalaSat/nostros/issues/518

Thankfully the people I was following were cached by amethyst, which restored them.

https://metadata.nostr.com seems to fix this, however I don't see a way to upload it's backup Json file.

There are other tools which will back up your nostr, I will post them in the replies.