I debugged this to the root cause of the actual issue. The root cause was line in OBSBasicPreview.cpp:

		size.x = float(obs_source_get_width(source) - crop.left - crop.right) * scale.x;
		size.y = float(obs_source_get_height(source) - crop.top - crop.bottom) * scale.y;

As you can see here, first it gets the width of the source: 1920, the default size of a color source. Then it subtracts the left crop size and the right crop size, which are both 1000. size.x thus should be -920, which is an invalid size value of course.

However, obs_source_get_width returns a uint32_t. While the member variables of the obs_sceneitem_crop structure are all int, the mix of signed and unsigned integers here caused the result of that equation to be 4294967216, i.e. an integer overflow.

This overflow would cause a near-infinite loop in DrawStripedLine() in OBSBasicPreview.cpp, which additionally has such bad perf to begin with that it just has no chance of ending any time soon. Perf fixes will additionally need to be deployed to help reduce mutex lock time.

I have fixed this in #11922, and I will also fix draw performance in this file in a subsequent PR.