Bizarre A4 keyboard issue

[Boydie]

Okay, this one has me flummoxed!

My A4 keyboard has developed a very weird fault. Pressing <FN> plus cursor keys moves the pointer, <FN> plus W or E produces Menu or Adjust. the Q key produces "q" or "Q" every time. Pressing Select on the mouse works.
Yet <FN> plus Q does nothing.

It used to, but now it's stopped.

What on earth???

Edit: Q works fine as Select, when locked into FB mode with <FN> <NUM LOCK>. It’s solely <FN> Q that won’t play. Rest of the keys seem to be okay.