Hello, I have same trouble.
But it all started yesterday after I updated Enpass through the repository. I have now Enpass 5.2.1
Before the update the sync as worked perfect with my default browsers chrome, since day one I installed Enpass some month back. But after last nights update of Enpass the sync button was red. It all seem to work but here is what happen:
I click on sync to drive, it opens a tab in chrome plus shows this text (as it should be):
"You have been redirected to drive login page. Please login there and allow Enpass to synch with your drive account"