Why the difference in choosing a seat?

[SYD]

It is a thing at T-80h when PCV comes into play. Within each status level, you can see a large variance in what seats are visible to each pax. Even within status levels, eg. platinum I've seen a variance between what's visible within T-80h and I have to resort to seating overrides to seat pax on separate PNRs together.

I’ve noticed that also. Since SYD+1 and I are both WP, being on the same PNR is not as important when it comes to seating but we do see odd things - especially on domestic routes. We normally select two adjacent aisle seats and I often have a lite shadow on the middle seat that SYD+1 can’t select but I can see free and EF shows empty (not blocked).

Although, next time I’ll try @justinbrett ‘s trick of using an EF account with no QF status to see if it’s actually a real shadow.