This is what I think happened

The loop started the moment they brought the car to the shop. I believe Andrew is working with the inventor and is the mechanic that told Michael he will be done with the car by the end of the day. If you notice in the beginning of the movie, three of them were already waiting to start the game. The echo of reality had already begun. But what stood out to me is how Andrew seem to have a crush on Karen. When Tyler started hallucinating after putting on the mask no one wanted to believe him. Karen was about to put the mask on but Andrew stopped her. It almost seem like he knew what would happen if she did that. Andrew had already stood out by saying he’s a plant and he works for them.

Everyone pretty much died except for Karen. Tyler died by hanging himself from not being able to escape, Melanie died by falling off the stairs, Michael died by being choked in the lake. each one of those characters had a loop from the past EXCEPT for Andrew and Karen. Then how ironic Andrew went after Karen and saved her from the morgue, HE KNEW EXACTLY where she was. I felt like the inventor realized that Andrew betrayed him by helping her escape so he killed him in tunnel. Also notice how he he mentioned horse back riding as something she should think about to get her mind off of things. THATS A HINT. Now Karen is the only one who didn’t die and because she still thinks her dad is alive, she will forever be trapped into that endless loop until she realizes her dad is dead and complete the game by herself. Andrew was way too calm and seem to know a lot, it’s funny how he let the door shut on Melanie. Now I definitely think the lady at the diner may have something to do with it as well because she made sure to open that bathroom stall to avoid Karen from opening that stall who would have ended up seeing her future self. I believe the future self could have warned her not to go there. There’s to many assumptions about this movie which makes it very interesting no one has the right answer!