Hi @Dan Hopper ,
Considering that the issue has followed the user in new Outlook profile and even a different laptop, I tend to assume it could be more related to the user's mailbox.
Does the user have a large number of folders in his mailbox?
Is the size of the mailbox way larger than the other users'?
If possible, you can try turning off Exchange cached mode and see if there would be any improvement in Online mode.
Additionally, below are links about some scenarios and possible solutions to performance issues in Outlook. You can take a look at them and see if anything can be applied to your situation.
- Outlook performance issues in a Cached Exchange Mode .ost or .pst file
- How to troubleshoot performance issues in Outlook
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