I don't work there, but I took a look at the source code and it appears that the dialog originates from here:

GitHub

primal-web-app/src/contexts/AccountContext.tsx at 870666becfa9e0e3adf0d7322e2ad788c799f3f1 · PrimalHQ/primal-web-app

Primal's web app for Nostr, as experienced on primal.net. - PrimalHQ/primal-web-app

Judging from the if-clause a few lines earlier, it does indeed check whether your updated follower list only has one account on it, and will display this dialog if it does. As to why that might happen, my best guess would be that the relay somehow returned an empty follow list. Not sure what the best way to fix it is, since apparently this DOES sometimes happen. Perhaps a less confusing message and different options would be helpful. I'm thinking something along the lines of "Something went wrong fetching your follower list" with the options of "Try again" and "Cancel".

I already lost all my following list once by accidentally clicking it and just want to be able to follow people haha Thanks for researching this!

Well, best advice I can give you for now is to just click "Abort" whenever this happens and then try again lol