I think I've narrowed it down a little. My issue seems to be clipboard related:
Let's say for example you're building a dungeon with UDL. You set up all the boundaries, maybe spawn a token and use Ctrl+L to test. No problem.
You then want to set up some torches for lit areas of the map. You spawn in a torch/lamp token and make it a source of light. Rather than repeating that process you copy the configured token and paste it in another location. This is where I notice performance issues; maybe it struggles when there are multiple sources of light and maybe my map has too many (approx. 8 torches?)
My main concern is how sluggish everything is, if you grab a token that can see light and emits light it takes several seconds for the map to update just moving a single grid space.
I might do what lavathor does, which is just use fog of war. Kind of sad since I purchased the Plus mainly for the dynamic light feature; guess I won't bother renewing my subscription.
Edit: I just did another test with Task Manager running in the background. I'm currently testing a map on my non-gaming laptop (Intel 630 GPU) and anytime a light source gets added my GPU gets pinned and the application freezes for several seconds. I think my current laptop doesn't meet minimum requirements to use UDL; I'll test on my gaming PC later today.