It turned out to be user error. I was closing Touch Portal down - or so I thought, but it was running in the background. Because the app doesn’t play nicely with desktop scaling (that monitor runs at 250%) it was almost invisible in the tool tray.
Once that was sorted, all became good, with the only remaining issue being the font sizes in the display on the tablet. The ones that were set to “auto” were WAY too big. Perhaps that’s another desktop scaling issue?
Anyway, it works brilliantly now. Thanks very much.