On 3 January 2019, prescribed vertical separation was lost between a Bombardier DHC8-400 and a Piaggio P180 on converging cruise tracks at FL 220 and only restored after a resulting TCAS RA was followed. The Investigation found both aircraft were being flown in accordance with their clearances and that the controller involved had not been aware of corresponding traffic and conflict alerting system activations. A specific traffic display fault which arose from failure to follow a routine software upgrade procedure correctly and the shift supervisor failing to recognise the need to act as controller when workload increased were assessed contributory.