I was wondering about this as well the other day. I use FSLTL as my injector, and I have the same issue. I’ll do a flight from A to B, traffic will be working, then do a turnaround and do B to A. On the turnaround, I’ll see traffic in the air, but once I arrive at my destination, there is no traffic on the ground at all. Once aircraft touch the ground they disappear. I find I have to completely restart MSFS to get it to work again, going back to the main menu doesn’t help.
So seems like this is just another Asobo AI traffic bug