Sent Email Not closing

Windows 10 All available updates completed successfully and Office 2010 also all updated completed.

I raised an issue and advised it is intermittent throughout the day, I have a PDF file (either on desktop, network location, etc.)

I click the mouse right button on file > send to > Mail recipient. An email would open showing PDF attached, I0 enter the email address and left mouse click on send. The email would stay opened and I would have to manually close the window, check sent items and confirm it was sent before moving onto the next email.

My office is repaired, I reinstalled it, I removed all updated and re-added windows updates. I checked and confirmed all outlook settings with a colleague who can work fine. The same computer builds and office applications. Upgraded on the same day. No issues with the old system.

There is no disabled add-in, basic windows add-ins switched on. I tried safe mode; nothing seems to resolve it. I would remote in, check settings and test. It would work and then I would email or call either 5 or 10 sometimes up to 30 minutes to advise the issue is back.

Me and 2 other colleagues are the only ones in office, they all turn over a large amount of data and forms, so I haven’t tried another computer/user swap yet… but I am wondering if anyone has ever come across this before? Is this just a random occurrence?? Can’t seem to find anything online regarding it…
Any information or ideas/hints would be appreciated. Thanks.