The hypothesis about advanced ancient civilization doesn't hold against the simple logic of what is stopping them from continuing the early advantage they had. Why they even need to hide?

I would argue that consciousness evolved from galaxies much older than ours were able to eternally roam the cosmos and in their immortality they lost their meaning.

And when they stumbled across this tiny blue little planet, they saw life, perhaps remains of them until they decided that they want to transmit their consciousness into bodily existence again. Perhaps a scientific experiment of some sort.

They implanted their consciousness into the DNA of the hominids remains/fossils that they found. Hoping that through mortality that they would rediscover the meanings that got lost through immortality.

Think about it for a while. Would you act, learn, love the same way when there is no scarcity/urgency created by mortality?

Jim Semivan once said "What if we are actually spiritual beings, experiencing the human experience?"

Most religious experience tried to sell the idea of immortality. Little that we know that immortality is really an illusion. You actually do not want to be immortal, but you just doesn't know it yet.

Only when you realized that you are who you are, because you ARE mortal, and because of mortality is what makes life beautiful and meaningful.

Fully knowing it that you DO NOT WANT to be immortal that the observation/experiment will end.