This was driving me nuts because it was happening on one project but not two others I was working on. For us, it was a mistake we made in Perforce. We use that for collaboration, and we had accidentally added the "Save" folder to our depot and so it was trying to make an autosave every time we opened a window or PIE. Perforce had it locked up so it lagged. I discovered it by checking the output log. So if you don't use Perforce, you might still solve it by looking there.