We have also been having this problem for some time now, though it appears to have stopped for a while.
It seems that the shift to Analytics from Pro has caused some issues with the API token validation from Google.
Having gone backwards and forwards with emails to Moz crew, I was finally directed to the Google Analytics validation link, where I was able to cancel the validation for Moz, then reapply for it from the Campaign Settings.
It seems to have had some problems with authorisation initially, but that appears to have stopped.
I hope this helps some.