Something I was wondering for some time, and from what I understand, this difficult point is quite known.
If only one present moment exists at a time, then it means that past no longer exists.
How causes in the past (which no longer exist) affect the mind now, in the present?
How can something non-existent be a cause for the present effect?
If cause is different from its effect, then there needs to be at least two moments to exist. One moment is cause, another moment is its effect. But does that cause itself causeless or does it itself has a cause? This would require infinite regress. We may say that cause and effect is found in one citta or one moment, but this would be self-causality where the citta is its own cause and effect.
Even if we accept that sum total and mixture of ALL causes and accumulations are passed from one citta to the next one, it still has a problem.
How does one citta that ceases in order for another one to arise pass all the accumulations if it has to cease for the next citta to arise and take them?
For the question it doesn't matter if one citta arises instantly after ceased citta, or if it arises and is the first citta after lets say 500 Aeons.
Even if we posit bhavaṅga-citta, or momentary ālaya-vijñāna, the question is still the same. How can accumulations be passed (from citta to citta, or from bhavaṅga to bhavaṅga) if one moment with all accumulations has to cease for the next moment to arise? If all accumulations cease with that citta or bhavaṅga, from where would the next citta or bhavaṅga take them?
One of the things could be that this is artificial breaking citta into "mind moments" is an abstraction that can create the above paradoxes. Maybe we shouldn't picture process of cittas as one domino falling causing the other to fall with there being only one domino that exists at a time. So how can only one existing domino that causes itself to fall exist?
What solutions do you see other then saying "don't speculate, just practice"?
"Life is a struggle. Life will throw curveballs at you, it will humble you, it will attempt to break you down. And just when you think things are starting to look up, life will smack you back down with ruthless indifference..."