The message body is not updated

Hello,

I have an application which edits the message body of the email. When the edit is done the change is pushed to Exchange server.

My problem is that Outlook 2021 is not able to update message body even I click on Send&Receive button. The body is only updated when I restart Outlook or when I try to edit the message in Outlook. When I edit the message I get the error :"The item cannot be saved because it was changed by another user or in another window". Then I return back and the message body is updated.

The app also updates PR_LAST_MODIFICATION_TIME and PR_CHANGE_KEY tag but body is still not updated.

The cache mode in Outlook is turned off.

I tried also change the body manually through another Outlook 2021 and the body is mostly updated in few seconds.

Outlook and Exchange are up to date.

Everything works fine with older versions of Outlook.

Do you have any idea what I am doing wrong?