Hi,
What's the specific version number of Outlook you are using? Please first make sure your Office and Windows are fully patched and then see whether this issue still continues.
Besides, do you use Lync or Skype for Business? If so, we may first try to close these communication software and then open Outlook to see whether the same issue happens.
We may also try performing a clean boot in Windows, then have a try and see if issue persists. This helps eliminate whether the issue was caused by any software conflicts.
Regards,
Steve Fan
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