Still no resolution from SQ. Four weeks ago I got a phone call from them, to tell me that they had referred the issue upwards, but the PPS value is still stuck at what it was in Jan 2020 (didn't even reset to zero at any time) and no follow up since. The chap on the phone agreed that it was strange that my Australia - UK trip in Jan/Feb this year hadn't credited at all, but he couldn't help. He also promised to highlight that I hadn't been credited the correct amount of KF miles, but this hasn't been fixed either.

Maybe they don't need to rely on customer loyalty any more under their new and significantly more expensive fare structure, but it's still a bit of a shabby way to treat people who have stuck with the airline for many years.