On this toon (and it seems only on this toon), the Undercity flight point no longer has any connections. This toon is from vanilla and has had no issues with the FP until some time around BFA. I can fly into UC but trying to fly out tells me I don’t know any flight points connected to this one.
I tried using the toy that teaches all the zone flight points but to no avail since I already “know” them all.
I have previously opened a GM ticket and was told to open a bug report (which I did). Currently the issue is ongoing.
Perhaps posting here will help.