Sorry, I wasn't sure if it was Kodi, LibreELEC or RPi issue so thought I'd ask in a few places. I wasn't sure how joined up these things were.
Thanks for your reply. At least I know my Pi 400 isn't the problem and I can fall back to using my Pi4 for Kodi.
The Pi 400 is brilliant though and a real throw-back to the Spectrum 48+ and BBC Electron computers I had growing up. Just incredible to think how much more powerful this thing is and much smaller too.