After successfully installing NoMachine on two other devices without complication, the install was retried on the problem machine and the issue was resolved by shuffling USB clients. The only unusual aspects of this client was that 1/ a native BT adapter (suffering poor range) was disabled, and a third party BT adapter (with better range) was connected externally, and 2/ a relatively high number of USB devices were connected using one USB2 hub and one USB3 hub. The only change was to move a keyboard USB client from an integrated USB port to one of the USB hubs and the conflict ceased.
If the conflict reappears, I’ll pursue your suggestion but it seems to be working properly for now. Thanks again.