With the skill menu open, I get a big framerate drop once a second. This is like a big stall in render, but appears on framerate monitor as a drop from 100fps average to 60fps average. Visually appears like everything pausing every second. Combining this with navigating skill plan catalog has caused a disconnect with game closing a few times.
While opening various UI elements does cause a stall (especially fitting menu), only the skill menu seems to have a persistent instability.