You have likely been logged out because we've been rolling out our new account authentication service over the past few weeks - this requires a new login to become active.
If you are running into issues, these pages might assist you:
If you're having trouble logging into the Fandom App (on iOS or Android), please try uninstalling then reinstalling the app.
See Introducing Fandom Auth - Our New Secure Login Service for background information on the changes. There are relatively few user-facing changes - primarily the addition of Apple ID as a login method, and some design updates to account management pages. Login sessions also now only last up to 6 months, instead of indefinitely.