Was your actual account's watchlist wiped?

If so I apologize, there is nothing that should've caused that. The only part that removes anything from the watchlist is when you remove a series, and even when you do remove a series from your watchlist it'll remove it from the current profile's watchlist that is stored in the browser, not the original account's watchlist.

Otherwise you'll need to visit https://www.crunchyroll.com/account/preferences and scroll down a bit then press the "Import Original Watchlist" button, I should probably make it use the current watchlist as the default on the first time creating a profile instead of creating a new list entirely.

If you have any more problems join the support discord or if you want to request a feature like this visit the Github and open an issue.