Hi,
How large is the OST file associated with your account?
Do you have the "Mail to keep offline" slider set to "All" under Account Settings? If so, try setting it to a short interval and see whether this issue continues.
Besides, if your Outlook shows "Updating Inbox 3.99 GB", please have a look at the following Microsoft KB article and try the resolution to fix the issue:
Status bar progress never shows more than 3.99 GB remaining on initial Sync of large folders
Hope this helps.
Regards,
Steve Fan
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