Files app doesn't recognise Google Drive - Authentication Required

Since updating my iPad (5th generation) to IOS 15, the Files app won’t recognise my Google Drive. In the Files app, I get the message “Authentication Required - you need to authenticate in Google Drive app”. There is also a link that takes me to Google Drive but it is already signed in and working. I’ve tried logging out, and re-installing both apps but nothing. Privacy Screen in the Google Drive settings is off. Any help appreciated.