Go to File > Options > Add-Ins. At bottom, click Go next to COM Add-ins, and see if you have the Send to Bluetooth Add-in enabled. I do not know if this is a default add-in on my HP zbook or where it came from, but after disabling it (uncheck), the paste now works as it should! (I use a screen capture program and do Ctrl-C, and then Ctrl-V into Outlook and whenever I did this into a new message or a replied to message, the clipboard was empty. Now this works again.)

I can confirm that this works for me as well. It was a most frustrating problem that I have just had to live with over the past couple of months. I practically live in Outlook, so it's been particularly bad.

Finally, I have my clipboard back!