"Possibly stuck in sync counter. This may lead to instabilities."

[Ryan Day]

Got a "Failed waiting for the material render to initialize" followed by exceptionally slow performance after editing the label on a glass material. Everytime I open the scene since I get "Possibly stuck in sync counter. This may lead to instabilities." followed by "Failed waiting for the material render to initialize" errors and performance is absolutely abysmal. I'm talking it takes 10 minutes for 'performance mode' to engage following these errors. I have a couple complex materials (beer with bubbles and a small scattering medium with a spots density map) but other than that this is a pretty simple scene. An identical scene, just with different textures but the same two complex materials, runs adequately.

Task Manager reports CPU usage anywhere between 14% and ~50%, usually mid 20s, while the scene is open.

Any ideas? It's absolutely useless to try to do anything with it like this; it either crashes or just simply doesn't do anything at all. Running an i7-4790k @ 4GHz.