I've noticed that as of a couple of days ago I can't access gmail in my web browser ( https://mail.google.com/ ) or using the Gmail app on my Android phone, but I can access it using BlueMail on my Android phone. Same behavior on my home and work computers.
Best guess is Bluemail is using IMAP, Google website and Gmail are using their API.
Before I spend time on this wondering if anyone else is seeing anything similar. I use PiHole for my network, but I've whitelisted mail.google.com with a wildcard match rule.