It’s been a bit of a problematic week for Google. In the last few days they’ve had a number of outages or problems across different services. There was a major outage of Google Calendar. All email, including some spam, was delivering to the primary tab instead of the correct tab. Additionally, Google postmaster tools hasn’t been updated in over a week.
Google apparently blamed the calendar outage on some congestion with their cloud platform. There’s been no comment on the filtering issue and the person who generally responds to mail issues hasn’t been as responsive as usual.
These outages could be completely unrelated, of course. But generally Google is a pretty solid platform so it seems suspicious that multiple services break around the same time. Whatever it is, it’s nothing you’re doing, it’s a problem on Google’s end.