Question: Same sort of issue with google calendar(s)
'Was just seeing the~same vexing problem with some google calendars, and utilizing them with macOS Calendar app, on HighSierra. 'Would enter my known-good google calendar account PW, but then be left with a blank window and only one option, to hit <cancel>.
Fortunately, the "fix" was also as ~simple (but non-intuitive) as to lock & unlock my login keychain, described previously in this same thread.
Unsure what initiated this problem, but maybe in the act of writing it down here, if/when it crops up again, i'll recall the solution.