Good I was right, but this is not a solution.
Now if you run top you may see that your example takes whole core of CPU. And enabling Graphics API Visual Indicator (in nvidia-settings) shows tens thousands of FPS.
I found that in Vital synth and in recent Waveform (11.5.18 12.0.xx) with GTX 970 and GTX 660.
Now i’m on old Radeon and that issue is partially here, Vital seems fine, but Waveform has always stalled GUI with OpenGL render.
It needs a real hardware to reproduce, yes.