Keyboard keys " and @ have suddenly become reversed on Kubuntu 21.10

I've been using a Bluetooth keyboard for over a year on the same system (Ubuntu Studio-Kubuntu 21.10).

A few days ago, I noticed that the " (Shift+2) and @ (Shift+') keys suddenly became reversed. I'm using UK English, so I tried adding US English, because it would be correct with that layout. The layout remained the same, except I was unable to type £ (Shift+3), as expected. But removing the US layout changed nothing. I tried other UK layout variants and they were of no help.I soldiered on with the problem until suddenly the 4 key was outputting 2.

I assumed a broken keyboard and have a brand new one now, similar model but updated version. In UK English I still have the swapped @ and ", but now the # key produces arg:3 in Konsole, blank everywhere else.

This is driving me insane, as these are my most used symbols in my daily work. Any pointers as to what I can do about it much appreciated.