iOS 18.6 Mail app: Recurring OAuth failure with Gmail accounts

I’m using an iPhone 14 Pro Max running iOS 18.6.1, and I’ve noticed a very frustrating recurring issue with Gmail accounts in Apple’s Mail app. When I add Gmail via Sign in with Google (OAuth):

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• It works perfectly for 2–4 days, syncing mail normally.
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• Then, I get an error: “Cannot Get Mail — the mail server ‘imap.gmail.com’ is not responding.”
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• From that point, Mail never recovers. Tapping to refresh does nothing.
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• The only way to restore functionality is to delete the account from Settings > Mail > Accounts, then re-add it via OAuth. It works again—until it fails again.
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This issue is exclusive to iOS Mail:

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• The Gmail app on the same device never has issues.
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• Apple Mail on my MacBook Pro also works fine.
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• I have two-factor authentication and a passkey set up—and those work everywhere else (web, Gmail app).
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What I’ve already tried:

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• Full reset of Mail (remove account, delete app, reboot, reinstall).
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• Resetting network settings.
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• Toggling Background App Refresh and Fetch/Push for Mail.
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• Verifying 2FA and passkey logins on web.
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• Confirming that there’s no unauthorized access in Google Security.
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Despite all that, the problem persists—every few days, Mail loses OAuth access and stops syncing.

This strongly suggests that Mail is failing to maintain or refresh its OAuth token on iOS 18.6.x. Apple, can you please investigate this issue in depth—particularly OAuth token handling, background refresh, and storage?

Happy to send device logs or enable diagnostics if there’s a profile or tool I can use.

[Re-Titled by Moderator]

Original Title: iOS 18.6 Mail App: Gmail OAuth Fails Every Few Days Until Re-Adding fixes it for an additional couple days