From time to time my Alt Gr button seems to stop working, which I use for several special characters like
Turns out the problem is related to the process mstsc.exe (Microsoft Windows Remote Desktop).
Solution: Close any RDP windows you have open (no need to logout, just close them). Voila, Alt Gr works as intended again. Now you can reopen them and hope it doesn't happen again.
You should also be aware of the temporary solution: Pressing CTRL + ALT is the same as Alt Gr - in case you can't close the current RDP windows for any reason.
This minor, yet very infuriating issue, has been present at my computer(s) for several years, both Windows 7 and Windows 10.