Thanks for your answer airflamesred. I didn’t see it earlier - I must have missed a notifications setting.
I don’t know if I identified the problem but it went away. I have opened the Kontakt a few times since without problems.
I did place the two dongles on different USB hubs at some stage, but I continue to have intermittent license failure for the Cubase one. I think it may be a USB problem as it gets corrected now by removing and reinserting the USB key. I am a bit worried how long the key will last if I keep having to remove and reinsert it though. I had it on a short cable to eliminate stress on the key itself, but have removed the cable now as a possible extra connection failure.