Arnold Zuboff makes a case for this in "One Self: The Logic of Experience" (Inquiry, 1990) [0]. He calls it universalism: there has only ever been one subject of experience.
One of his thought experiments: imagine a meteorite is about to wipe out all life around you right now, instantly. If this exact experience - being you, here, thinking this - is instantiated anywhere else in the universe, it will continue there without any gaps.
Hindu mystics were already exploring and articulating these non-dual concepts in great detail thousands of years ago, in the Upanishads. As Robert Jastrow would say:
"For the scientist who has lived by his faith in the power of reason, the story ends like a bad dream. He has scaled the mountains of ignorance, he is about to conquer the highest peak; as he pulls himself over the final rock, he is greeted by a band of theologians who have been sitting there for centuries."
Apocatastasis
The thesis goes something like: God is timeless. Time is necessary for change. In order to experience change, God creates universes that have time and descends into these lower states of existence. This gives rise to conscious beings - they’re literally small disconnected slices of God that descended to our state of existence. When you die, you “roll up” back into God taking your lived experience with you.
He was posthumously condemned in 1225 with an order for his books to be burned.
Edit: I wrote this response before you added that this was specific to the theology of John Scotus Eriugena.
Edit: Ah, yeah, this was just one thinker. Early catholic thought is diverse and fascinating. A lot of work went into reconciling religion (and the rest of society really) with the “science” of the time. There is a lot of fun exploratory work trying to reconcile Catholicism with other philosophies, only some of which became cannon. It’s one of the reasons why the scientific revolution was so jarring for all of society - it threw thousands of years of convergent philosophy across society into a paradigm shift when we were forced to abandon things like the 4 element theory.
A decision is a reaction from an observer: and it requires information and feedback. Is the thing that decides special? Is it the same thing as everyone else's?
If you can imagine it, does it make it more likely? Only time tells.
My intuition for all sentience between "fragments" of a single consciousness from outside the universe was that, if Free Will™ is real, then true randomness can only come from outside a system..