Mail from particular sender not appearing in mail box

Gmail suddenly deleted a large number of messages from a dedicated mailbox. Now I see my friend is sending messages (indicated by the number column) but none of them are in the mailbox to be read.

I checked online, and none of them are in the Inbox on my Gmail account. It indicates 95 new messages, of which I can see about ten. So apparently messages are being delivered invisibly.

Apple support says it's a Google problem.