same issue - additional troubleshooting info
I am experiencing the same issue. As a test, I created a new account on my Mac, setup Mail, and found a message with an ICS invite.
The event showed on the correct date in Calendar.
I went back to my other Mac account and deleted Calendar prefs and caches from the user Library folder, but this did not address the issue.
I think next I will login using the test account on my Mac and rename the Library folder of my main account. When I log back into my main mac account a fresh Library folder will be created.
Then I can migrate items from the Library folder piecemeal as needed (such as the Safari folder)