Calendar App on MacOS Won’t Sync After 5PM

I have a rather odd problem with my mac… None of my 4 Google calendars (2 gsuite, 2 normal) sync properly after around 5PM. The Calendar UI only shows The server responded with an error.

I've tried:

• Clearing the calendar app cache following this procedure
• Removing and re-adding these accounts entirely
• Entirely removing ~/Library/Caches
• NVRAM and SMC reset
• Upgrading the entire system from Catalina to Mojave

The only clue I have is this line from logs is:

CoreDAVPropFindTask failed: Error Domain=CoreDAVHTTPStatusErrorDomain Code=403 "(null)"

But still no love. Does anyone have any ideas? This is one of the more bizarre computer problems I've ever had.