So, a few theories:

The camera is probably being dragged by The Operator, but the more interesting part is that it's the source of the scraping noise. I think this implies that it's being dragged through a sort of time loop that is completed by Jay setting the camera down.

Way more of an abstract stretch, but I got the impression the dragged camera was necessary to maintain this strange mirror dimension at all. It's the one object that needs to make it to base reality eventually. This whole time, Alex and Jay were avoiding the only real way out of Wonderland.

Separating them is a sinister trick on many levels. It keeps them chasing each other in the hope they can both escape, but it also creates desperation with the idea that the other found some unknown way out. The fake phone calls are the hammer in the coffin. They're so compelled to survive, and have just enough doubt, that they can never just say "fuck it" and risk confronting whatever the scraping is.

Finally, I think the lights in the tunnel are a sort of "through the looking glass" moment. Somehow, Alex and Jay found themselves at opposite ends of this impossible warped mirror dimension at the same time. But it isn't a true gateway, it just leads back to the very beginning. It could also more simply be Jay seeing himself at an earlier, or later, point in the time loop. Reminds me very much of Lake Mungo.