Details would help.

Was it an OLTA or a real live human travel agent?

This was an AA ticket paid with money for a RTW fare, right? Was EDI the starting and ending point?

I'm confused about exactly what flights were cancelled (by the airline? HKG to TYO?) and how Vietnam enters into this. It sounds like some of the itinerary was (voluntarily if based on a rumor that Vietnam would close its border in the future?) cancelled or rebooked by the OP.

Why were the BA flights (from WHERE?) to LHR and then EDI purchased? Did the OP try to get the TA and/or AA to rebook the ticket after whatever flight was cancelled?