Logitech Combo Touch keys intermittently fail on iPad Pro

I have a Logitech Combo Touch keypad to use with my iPad Pro 12.9 running 26.1.

Recently I've noticed that when I type a selection of letters on the keypad they don't appear on the iPad. For what it's worth, the letters are s, t and j. I did a search about this and one suggestion was to toggle on and off full keyboard in the accessibility part of settings. That worked. For a while. Then it came back. I then upgraded my iPad to Tahoe, and the keys worked again. But now they have once again stopped working. Switching full keyboard on and off no longer resolves this so I thought I'd see if anyone else has come across this and knows why it's happening? My first assumption was that it was a keypad issue and hence to contact Logitech, but the fact that it is OS changes that I've made which have fixed it previously suggests it is more likely to be an Apple thing.