I have collected 15 daedric artifacts, trust me I've plotted the process out and went for them all specifically. However, I have not received the PS4 trophy for the Oblivion Walker. Is this a known issue? Will it soon be fixed? I am trying to go for Platniun and really don't want to start a new game just because I didn't get the trophy the first time around.

PS4 Version of Skyrim has the same bugs that PS3 had. Which means you probably need to do the same workarounds for this trophy. There are few advises floating somewhere, but let me give you the one I remember.

Get 16 Daedric Artifacts for the trophy to pop. You need to get both from the quest with werewolf. First save him and get the ring from Hircine and then kill him for the hide. If you killed him on your current save and not saved him... I am sorry, no rescue probably.

There are some other rumors about it. I remember three. Azura's Dark Star don't count, which I don't think is the case, but who knows.... Skeleton Key do not count, but it is necessary to finish it's quest for a trophy to pop. Order in which you get your Daedric Weapons matter for the trophy pop.

Good luck!