Have you restarted your system? That sometimes fixes this sort of issue when dedicated function keys on wireless keyboards stop working. Also, check the state of your batteries which, if really weak, can trigger all sorts of peculiar behaviors.
If all that fails, I'd get the freshest device driver and/or application software for the make/model in question and install that.
Brian - Windows 10 Home, 64-Bit, Version 1809, Build 17763
Explanations exist; they have existed for all time; there is always a well-known solution to every human problem — neat, plausible, and wrong.
~ H.L. Mencken, AKA The Sage of Baltimore