A theory or two (JMO of course). Based on MW-T video, and in contrast to my earlier scepticism about him being in the mountains at all:
Jay steals a watch from person unknown, either put up to it by the two AieBnB men, or because he knows/believes they will buy it from him once he’s done it.
He goes back to the AirBnB where they’ve told him they have the money for it.
The transaction goes wrong somehow: maybe they refuse to pay him and threaten him, maybe he tries to take both the watch and the money.
(This must be after the cigarette/steps pic, presumably.)
Jay leaves in a hurry, corroborated by the (now 3 according to MWT) witnesses in Masca.
He gets lost, in the area MWT claims to have pinpointed on the map, rings/facetimes (I’m still not 109% which) Brad, rings Lucy, has some misadventure or is caught up with by the AirBnb men. Bad result ensues whichever.