Hi @Sam Aruti ,
Based on my tests on Outlook 365 version 2105 (Build 14014.20002 Click to Run) Beta Channel, I could move the items normally from my Inbox to another manually(drag the item from inbox to another folder directly), so the issue may be related to your account or client iteself.
What's the type of your account(pop,imap or exchange), in order to further confirm if your issue is related to your client, it's suggested to log into your web mail and move same messages there to check if you could move them normally.
If it could work normally on your web mail, the issue may be related to your client itself, considering the issue occurred only recently, have you performed any specific operations before it? And what's folder that you would like to move the messages to (a folder in your account, a folder in other account or public folder )?
If you indeed move the item under your account, considering you have re-build the data file, in order to avoid the interference of corrupted Outlook profile, it's suggested to re-create a new Outlook profile and readd your account to check if the issue has any difference(Control panel>mail>show profiles>Add>readd your account).
According to your .ost file, did others who has similar size of data file in your organization also have this issue on their Outlook? If so, considering the data file limit may also cause this issue, it's suggested to check your size limit policy by this path in your register editor: HKEY_CURRENT_USER \ Software \ Policies \ Microsoft \ Office \ 16.0 \ Outlook \ PST
Also, if you work with a .pst file except your .ost file, considering corrupted .pst file may cause it, it's suggested to repair your .pst to check. And if you actually move the item under other account, please kindly check the permission assigned to you.
Besides, if you couldn't move the item on web mail, the issue may be related to your account, it's suggested to contact your mailbox admin to get more help.
Hope that would be helpful to you.
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