Brian Kramer,
Interesting. So follow me here. My computer, "A" connects to "B" and the enter, shift, alt keys don't work. I can open On Screen Keyboard, OSK, on the remote computer B and the keys work that way.
So I then use "A" to connect to "C" and I have the same keyboard issues.
When "C" connects to "B", there are no keyboard issues, which I would then agree with Conrad that there is a problem with computer "A".
The thing is, I have no idea what it could be. Other remote viewing programs have no issue, ie. Chrome Remote, TeamV, UltraViewer. I also tried replacing the keyboard. Maybe I'll try closing programs one by one. But I did record a video reproducing the problem.