SQ changed our seats on all four of our flights recently, only notifying us once. All whY redemptions for a family of 4 (2A, 2C), all seats selected at booking up to 5-8 months ago. Departure times brought forward 5mins for the SIN-KUL leg and 30mins and then again 10mins for the PEN-SIN leg.
BNE-SIN: selected 52C, received 69G
SIN-KUL: selected 47C, received 53H (this was the only one notified)
PEN-SIN: selected 51H, received 52K.
SIN-BNE: selected 49G, received 62G
Whilst we were not separated, the seats for the "long legs" were much further up the back and thus worse, especially for boarding and deplaning. I'll provide feedback as requested via the SQ email, mainly to suggest why bother with seat selection if it is not guaranteed and can be changed for any old reason.
This may have been avoided with online checkin but I don't usually bother with online checkin if I have access to priority checkin. As our outbound flight included a separate CBR-BNE leg, I did try the auto-checkin feature for the BNE-SIN leg. Printed off the bag tags and ended up using priority anyway. Not unrelated, they lost my golf clubs/bag between oversize luggage and SIN too but managed have it delivered to my accommodation the same night which avoided a missed tee time early the next day.
Also, I think they really need to make a distinction for benefits to SG and WP members, especially for lounge access. For eg, WP could use SKL or, better for my situation, WP can have more guests.