I’ve notice that I play the game at about 1/2 or 1/3 speed even at x4 speed, but sometimes it will rapidly speed up until I place down a new unit.
So I started experimenting and realized that if I place a unit down and then sell it, all lag vanishes and my game plays at the proper speed. Though I don’t understand why this is happening. You can experiment if it happens for you as well by placing 6 archers, running some enemies, placing a Cleric and then selling it.