Why aren't all emails showing through IMAP in the iOS Mail app?

Question

gmail

First, to avoid the most primitive questions, I would like you to understand that on the Gmail server, all letters are in place - both in "inbox" and in "all mail". No problem. I know how to move, search, delete and restore them . The problem is deeper, and I can't find a solution for it anywhere.

Through any browsers and the native Gmail application for iPhone, everything is also perfectly visible - you can read, reply, upload documents, move. No problem.

Through the built-in "Mail" applications on MacOS (I have two laptops), everything also works fine in IMAP. All messages are downloaded, visible, moved, you can reply, download attachments, and so on. Only one thing is

not working correctly -any mail application for iOS (except for the native Gmail application voiced above). And the built-in iPhone mail, and Spark, and everyone else for some reason do not download messages from January 1, 2016 to May 14, 2020 . This is what I cannot understand.

Moreover, for example, if you go to Gmail through a browser and force any message from the "hidden" period to be unread, then the Mail program for iOS sees that there is an unread message, but cannot show it in any way - neither with a filter, nor scrolling, no way.

Reinstalling the Mail app on iPhone doesn't help. Reconnecting Gmail account does not help. And it's not the device itself, because I tried to set up an account on another iPhone - the same nonsense.

That is, as I can assume, the point is in some system designations of messages for the specified period. Some hidden texts that phones perceive in such a way that they do not download messages from the server.

Another oddity. Some messages from the specified period can be found using the search. But not all.

Answer 1

Actually, great, of course. Someone immediately voted that the question was simple, but no one bothered to answer. )))) Except for Kelv13, who actually didn't answer yet, but only suggested. Well done.
Why is the question so simple if no one knows the solution?!))))

Answer 2

Gmail has restrictions on uploading data from the service, and different for pop and imap. Did you just wait a day or two?
Well, just tritely try disabling imap in the gmail settings and turning it back on - I remember that some time ago there was a problem with uploading mail from gmail, which was solved in this way.