Outlook for Mac Gmail Inbox Emails Disappear After Syncing

Environment: MacBook Pro running the latest version of macOS Tahoe, with the latest available version of Microsoft Outlook installed from the Mac App Store.

A Gmail account in Outlook for Mac is not syncing/displaying the Inbox correctly. The Gmail account contains approximately 13,500 emails in the Inbox, all of which are visible and searchable through Gmail online and on the user's phone.

Outlook will initially download and display some or many of the emails, but they later disappear and the Inbox suddenly shows as completely empty. Sometimes only a small number of recent emails appear, and clicking messages or switching between folders can cause additional emails to suddenly appear. The problem then returns, often after restarting Outlook or by the following day.

Troubleshooting already completed:

• Confirmed all emails and folders are present and working correctly in Gmail online.
• Removed and re-added the Google account to Outlook.
• Reset the Outlook account.
• Created a completely new Outlook profile.
• Tested both New and Legacy Outlook.
• Updated Outlook to the latest available version from the Mac App Store.
• Restarted the Mac several times.
• Completely removed Outlook and moved the existing Outlook profile, database and preference files out of the Microsoft Group Container.
• Reinstalled Outlook from the Mac App Store and created a completely fresh Outlook profile.
• Re-authenticated the Gmail account using Google sign-in and allowed Outlook to rebuild the mailbox entirely from Google's servers.
• Tested Gmail's IMAP folder-size settings.
• Tested the same Gmail account in Thunderbird. Thunderbird successfully downloaded and displayed the mailbox correctly.

After the completely clean Outlook installation, emails once again started downloading and appearing in the Inbox. However, by the following morning, the Inbox was completely empty again, despite all messages remaining safely available in Gmail.

The same Gmail account works correctly through Gmail online, on the iPhone and in Thunderbird email client app. The problem therefore appears to be specific to Outlook for Mac synchronisation/display of this Gmail mailbox on macOS Tahoe, rather than a problem with the Gmail account, server data or previous Outlook profile/cache.