My idea was to show who things work, rather than do any kind of textbook explanation. That said, I understand why this slow-down is mysterious (and deserves a better visualisation).
Thanks for info. Tiles are on CSV and the animation is on Canvas; I will try to see what's the problem (don't own anything with Android, though). In any case: I would be really, really grateful for creating an issue here: https://github.com/stared/quantum-game/issues.