It can happen when switching between clients. Iris has "Follow all" button that helps to get your following back up. Nostrgram.co has a history feature that may restore the original list.
Discussion
Interesting. Good to know!
Sometimes I have various clients open, at the same time. Just to take advantage of different benefits. But I lost the accounts I follow, many times. Thanks for the "Follow all" feature - one click to follow everyone my favorite nostr profiles are following! Essential to recover from this annoying bug quickly 🤙
happened the same to me