Gmail inbox empty on ios mail app / ipad

I use the standard mail app on my ipad and configured an gmail account in it.

from time to time the gmail “inbox” appears as empty, whereas there a few hundreds emails in it.

A search in the top menu for all messages in all inboxes with e.g the letter “a” gives me all inbox messages with an “a” in it also those from the gmail inbox . The inbox under the gmail remains empty.

One way to temporary fix it is to go to settings , deselect mail for the gmail account and reselect the mail for the gmail account. The email inbox for gmail is correct again. Until the problem reappears...

any clues?

Ps: software version is ipados 13.3.1 ( the latest available for me)