This is a very odd bug, but I've reproduced it a dozen times under my current project and I'm fairly confident in reporting it despite how odd it might sound. From what I can tell, tiles towards the top side of the isometric map cause DreamSeeker to stutter and perform poorly.
As shown.

Moving around anywhere near the top of the map will create this problem. Everything client side will begin to slow down, as witnessed in animate() calls stuttering, pixel movement dragging and generalized slowness.
Numbered Steps to Reproduce Problem:
Moving any area of the game, no matter how many tiles or objects therein to the top side of the map will cause significant performance loss. Moving them to the bottom half of the map, ie on the opposite side, eliminates the issue completely.
I've played around trying to reproduce it in a test project independent of our branch with no luck. That being said, this odd behavior must be some strange interaction, as even a small, 8x8 patch of barren turf at the top of the map performs poorly when compared to the same patch placed at the bottom.