Hi @Dinesh Vinay ,
Based on your description, I have some questions to help us narrow down the issue:
1.Have you tried logging in via OWA? What mode are users using, cached or online?
2.Have you tried to use problematic user account to log in outlook with any non-problematic user's computer to see if the problem persists?
If yes, you can try to recreate the Outlook profile. Here is the article for your reference: Create an Outlook profile - Microsoft Support
If not, it could be specific client-side issue. Please provide us with detailed information about Outlook client version and make sure you have installed the latest Windows and Office updates.
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