whats the deal with the other Ryan?
why only Ryan and Tree experience time loops?
I agree. The other Ryan is never explained. And why did he have to kill the real Ryan in this timeline quickly... just never explored.
My best guess is just that some experiment in another parallel world somehow involving a completely different set of issues was the beginning. And then she shoots into another timeline starting on her own adventure. And this is what the movie decided to follow...odd way of telling a story. But, from a certain point of view, quite befitting for a tale of many-worlds.