Old Nov 8, 19, 11:46 am
FlyerTalk Evangelist
Join Date: Jun 2015
Location: SFO/SJC, BWI
Programs: :rolleyes:, DL DM, Mlife Plat, TR 7*, SPG/MR Plat, UA 1K
Posts: 10,823
The seat map is frequently greyed out (well, previously, no idea if it's still grey after the latest palette change)/blocked on an existing booking for cabins other than the one you're ticketed in.

This first happening routinely in 2017:

Another Negative Change by Delta: Blocking Seat Maps for Other Cabins

although as you've seen if there's a buy up offer then they show you what's available. But it can come and go randomly.

In short, to paraphrase the saying, don't ascribe to malice that which can be attributed to poor/random IT behavior. It's not a nefarious plot.

(And BTW a more reliable indicator of a waitlisted certificate clearing is if you had the duplicate segment previously and then the whole segment disappears)
Zorak is offline