Not sure about other clients, but I seem to remember Primal being one of the worst about nuking follow lists.

This may be related to how the Primal client works when compared with other Nostr clients. Most Nostr clients check for your relay list from one or more popular indexer relays, which pull these lists in from other known relays, then look for all your other notes from the relays you listed. This way the clients are looking for your notes where YOU have stated they should be able to be found.

Primal doesn't do this. Instead, the clients only read from Primal's caching server, which itself attempts to aggregate all notes from all known relays. If your follow list, which is just a kind 3 note, never makes it onto Primal's caching server for whatever reason, the Primal app is not going to look for it on your relays at all. It's just going to create a new follow list for you, overwriting your old one on the relays you normally write to.