Aliens.

The first movie already established a time loop by the original trio stumbling upon the Parr house when it already had been burned down prior. They also couldn't find their way out no matter how hard they tried so thus, if they stumbled across the Parr house, they surely were transported back in time when it stood.

The witch clearly manipulates time as shown multiple times throughout this movie.

Lane and Talia saying they had been gone for five days without sunlight.
Their alarm waking up them early and it still be night.
Lane looking like an old man when Lisa comes across him and he says "You look just like how I remembered."

There is clearly time manipulation going on or they've been transported into a time loop by the Witch herself. The video at the beginning is basically themselves watching their demise.

The GPS/watch and everything else was not going to work with them being under the Witch's powers and influence so of course, they weren't going to find their way out. Did Heather and the other two find their way out? No, they were stuck in the woods and it's clearly and even spelled out what's stalking them in all three movies is indeed supernatural and not aliens.

The lights have been hinted at rapid sunlight to darkness by the witch.

Lane described Elly Kedward being tortured by having rocks applied to her limbs which caused to stretch so thus, the creature bears the description of Elly's demise and no matter how the filmmakers portrayed her or want to backtrack, it is indeed Elly.

The stick figure being a human voodoo doll is clearly associated with witchcraft.

The mythology of the three movies mentions several instances where it classifies what's haunting the woods is supernatural, not alien. Coffin Rock, Rustin Parr, the missing children, Mary Brown's encounter with the witch, the first film, Book of Shadows (although cannon, still features the supernatural/ghost element.)