EDITED I believe this issue concerns several unique vendor objects, such as market stalls, from various packs. The following objects are no longer functional/interactable and don't spawn a vendor...
Ideas
In a new save, no mod or CC, the vendor next to the Equestrian Center never appear and the stall is always closed.
I have that issue too. The stall is in between Dukes Hall and the Equestrian Center. Mine has a purple sign with apples on it. I played from Wednesday 1st week of autumn to Wednesday 2nd week of autumn (autumn is 2 weeks long) on a combination of speed 1,2 and 3. I loaded in through Champion's Grove Lot. And the vendor never showed up.
It is probably not the stall itself, the one at the Roomies house (parched prospect neighborhood in oasis springs) was open when I checked that one after.
