Outlook running super slowly after syncing with exchange

Question

I am seeing a weird issue in Outlook 2016.

I have User1, User2, Computer1, Computer2.

User1 on Computer1

• Outlook works as normal, but ocasionally seeing unread message notification in folder panel with no new messages in inbox.
• To fix the above, user is scrolling to the bottom of the inbox and clicking Click here to view more on Microsoft Exchange
• After clicking that link, the messages all load, but from then on Outlook is super slow - clicking on an email takes ~1-2 minutes to view. It is unusable.

User1 on Computer2

• This works perfectly - there is no click here to view more on microsoft exchange message. No speed issues - all messages appear in inbox.

User2 on Computer2

• seeing the same issue as first scenario

what I have tried

• I compared add-ins - the are all the same for the users and computers
• Tried running in /safe mode - user fails to to login to the domain so can't test
• Tried running with /cleanviews - no difference
• Changing cache exchange mode settings from 12 months to all, and also tried disabling entirely - this appears to load the messages but outlook runs super slowly

what i noticed

• The exchange cache settings are identical for all scenarios.
• Under the Folder tab, the View on Server option is greyed out in cases where Outlook is working well. When seeing the issue, I am able to click this, at which point Outlook runs super slowly

How is this even possible? It appears to not be a computer setting OR a user setting, as the same user is only experiencing it on 1 computer, yet a different user gets the same on a machine where user1 doesn't get the issue.

Is there a way to get all outlook setting (maybe via a script) and compare with those retrieved from another machine?

If not - how can I possible troubleshoot this issue?

Any advice is much appreciated.