The Clothes!

We are used to people in horror films making bad decisions in the heat of the moment but this is stretching it. Usually in these types of films, we know the people are in a loop but they don't until it is too late. Having them discover they get killed early on and they still stay there, wearing the same clothes and making the same decisions? Really? Even when they were writing the note it didn't dawn on either of them that it was the same note? I can understand the character with schizophrenia getting the lines blurred but not the rest of them.

Yeah, it occurred to me that all of the characters were going to great lengths to "break the cycle" -- what if it was as simple as putting on a different shirt?

How is it a multiverse? What decides which universe you're in? Are you always bound to a certain "frame" of time? I may ask more soon.... There are plenty of ways that your multiverse theory can work. The movie does and doesn't lend itself to that possibility. Changing clothes IS a logical if not the most logical solution after isolation or exile, from their perspectives. Having different clothes changes everything because such a minor change means the previous loops are different. Also you miscalculated, you didn't account for the time a conversation, as well as, the act of changing clothes. Everything after that point has a equal if not greater chance to ensure the events never happened. This is an...interesting thought, there was still the Michael from the previous loop(s). How would he react to the fact he some how for no logical reason is in a different loop. One could say the change means you don't die in the mine or during those couple of days. Does Micheal still snap? If he does, is he violent still? If most or all live do the run into themselves the next day?
Mulitversal travel doesn't explain the bodies, the "at least two Micheal's", or especially the two Lyla's and the metaphysical subplot. At what point does the loop intersect to create "the retcon"? Also the multiverse, like time travel is a theory. As you should know time travel itself is not even a really a theory it's more of an idea. We don't know enough about time, "exotic" energies, and gravity. If you travel the planet enough you time travel, if you go to space you time travel, if you are moving and another is stationary that is time travel. This has all been proven, at what point do you just call it travelling? You also didn't account for the amount of energy it would take to have a physical being travel to another universe, or remain the same as reality seamlessly alters around them. How was this loop, the movie, different? Why did Lyla live?
After talking about this pseudo-scientifically, I'm starting to think the time travel is magic, not advanced science. I have studied the "occult", and "science", especially quantum gravity. The movie never makes clear if this is a magic or science story. The most likely answer is it's supposed to be both. There are arguably more instances of magic than science. What is THE moment of time travel you speak of? To stop a paradox one must create another more complex paradox through willpower, that's what I gathered after applying your theory. Strangely enough, that may be the intended ending. If all Lyla's are the same each time, while including the multiverse, does the ending we see always happen? Every answer raises more questions. Snake eating its tail, indeed....

After throwing a machete through a guys chest, "Stick around!"- Dutch (Predator)