You’re welcome, I know it’s not perfect unfortunately, this is the best workaround I found (I was in a hurry because I needed it for a game jam).
I learned that these small errors could be due to how computers work: nothing really happens “at the same time”, there’s always some latency between tasks (and this latency could vary, so the result can be different every time you play it)
Just a curiosity that I discovered while I was looking for a solution:
In Nier Automata to keep the audio tracks synced (switching between the 8 bit version and the regular one) they used a four channel track and lowered/increased the volume of two channels at a time.
The developer said that the more they played the more the soundtracks were going out of sync (for the reason I mentioned before), so they had to implement this workaround.