Hi,
What's the version of your Outlook client? (File > Office Account > About Outlook). Please make sure you have upgraded your Outlook to the latest version.
To check whether this is a client issue or a account server issue, please try to configure other accounts with no problems on these problematic computers to see if this problem will occur.
A corrupted profile may be the cause, please try creating and using a new Outlook profile via Control Panel > Mail > Show profile and see if there is any difference.
And then there could be some add-ins in your Outlook client that cause this issue, so it is suggested to start your Outlook in safe mode (Press Win + R, type “outlook /safe”, press Enter.) and see if the issue continues.
Besdies, it is also suggested to temporarily turn off your antivirus software to check if the issue will be gone, because some antivirus programs perform email scanning may cause this issue.
Hope this can be helpful.
Regards,
Aidan Wang
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