I don’t know if this is typical but on a few occasions before Christmas the ANA tool was showing seats on SQ, AMS – SIN in C as available. When I tried to book the ICC agent confirmed the availability but his system would not let him book the flight, he said something about the seats being reserved for other * or SQ ff members.
How not to go is via IST, DXB and SIN, I left LGW for AMS (via Eindhoven) on 20/12 and eventually arrived in BKK, midday 22/12.