Originally Posted by
SATCO
Did NAS simply find the duplicate waypoint and double-back the entire FPL to the ENTRY waypoint, from which it couldn't determine an onwards route?
It wasn't NAS, it's a completely different system.
That explanation in the report isn't clear but it seems to have found the Entry Point but not the Exit Point. If it can't find the Exit Point it apparently then searches for Waypoints beyond the border, presumably stepping out a step each time it doesn't find any of those in the plan. It found one of those in the plan but, because the waypoint in the plan was a duplicate of one surrounding the UK FIR, became confused because that waypoint wasn't correct in a geographical context.
Any system that just goes round in circles would be an issue, if NAS did nothing else would get processed so it would affect everybody. NAS will only go around the loop a limited number of time before stopping itself. Stopping the whole system is usually preferable to being stuck in a loop which is why most ATC systems will do that as the last resort. FPRSA doesn't seem to have been stuck in a loop but still applied that approach.