I'm back in house and have gone through my printer. Measured continuity, checked connections, measured temperature wiggled heater and the thermocouple.
Moving the print head about and checking connections did not give any results.
Could not find any problems.
It may have been a bad connection, electrical interference, earlier Cura models not being compatible....
Started printer and all is well - have printed several different prints and they run through to the end and turn out normal.
Great relief and great frustration not to know what really happened. For the time being I settle for bad connection in screw connector on top of printing head - most probable I think.
I learned one thing though, the temperature measured is about 6% off the real temperature of the Al head/nozzle.
Thanks for your suggestions.