If you're up for further testing, there's some thing you can try:
Download and install the
Consumption addon
Once in-game, type
/con profiling on
Then type
/con graph nibRealUI
Should see a graph appear in the center of the screen. If nibRealUI is causing the hangs, then the graph should spike to way above 1, possibly up into the 10 region. If not, it will stay low usually < 1.
Important: Once finished with testing, type
/con profiling off. Don't want to leave CPU profiling enabled as it uses up CPU time itself.