Did the emails disappear before your eyes? I know that sounds like an odd question but emails that appear momentarily and then disappear usually means they’ve been deleted somewhere and the view you’re seeing is catching up.
In this case the account might’ve been compromised (or at least accessed by someone else) and deleted from a different device.
I’m not sure if Google offers this functionality but are you able to see login activity? If so, check that all activity matches the IP addresses of devices you own.
If they were all just absent entirely when you logged in, then it suggests it might be issues on the server side.
Batch editing/moving/deleting emails isn’t something you’d easily do by accident but at the same time, if some emails are visible still and some not, it suggests it’s unlikely to be server problems. This would typically make all emails inaccessible.
