I have also had SQ flights, booked on website with my KF account not post, but not frequently. I have found partner activity such as hotel and rental car to be very hit and miss ans usually more miss. Take Kempinski, every time I stay at one I'll have to wait 6-8 weeks and then file a retro claim for 500mls. Now waiting for some credit from Connex which is a limo / transport service platform I used for a trip to Vietnam and that is a KF partner (is offered as an add on from SQ's booking / manage booking site). We shall see, not holding my breath.

However, if you want to talk about atrocious posting reliability look no further than KrisFlyerSpree where miles postings can take 3-6 months after transaction completes and often have issues. Gave up on that one a long time ago.