My wife has a strange issue with Apple Mail on iOS 16. Her Gmail inbox shows the five or six most recent emails (from today) and then the list of emails jumps back six months to last September and continues backward from there. Everything in between last September and a few hours ago is not shown in the inbox on Apple Mail; also not in All Mail.
There’s no issue like this on Apple Mail on Ventura or on the Gmail website. After repeated reboots, several rounds of Gmail account deletion from the phone and adding it back, it nothing changes. Perhaps there’s a corrupted index file somewhere in the background on the phone.
I installed the Gmail client on the phone, which displays everything normally.
(Happened right after, but probably not related to the rapid security response 16.4(a) that Apple issued yesterday; but with Apple one never knows…)
It sounds like the sync is getting stuck somehow. It’s really annoying that deleting the email account on the iPhone and adding it back didn’t clear it up, but it’s very possible the phone is holding on to data even when the account is removed.
Are there a lot of email messages in the inbox? Google’s sync help suggests one fix: “In your Gmail IMAP settings, set IMAP to only sync folders with 10,000 emails or fewer.”
You could also try deleting the entire Mail app itself. Then reinstall it, and then add the Gmail account. That might kick something loose.
Also: is she running out of free space on the iPhone? I have seen that cause really weird problems.
Problem is now occurring with Apple Mail on iPadOS and iOS (both 16.x) with exactly the same gap. (No problem on Gmail app and no problem on mail.google.com, and no problem on Ventura.)
Not a lot of messages; < 3,000
Plenty of room on the phone and iPad
I don’t think the problem is Googles. I think it’s probably, as you say, something in the background that is syncing between iPad and iPhone via iCloud. That this doesn’t occur with Mail on Ventura is odd, of course.