For me it looks like it starts and calculating substance only for the main monitor. As soon as i load a file or create a new one on the second monitor it crash. also worth to note, if i open a file on the main monitor and dropping it to the second one it seems to work even in full screen. If i close the window, so it will open at start on the second monitor it instantly freezing and crashes.
I also took some more time switching substance from main to second monitor and revers and noticed it don't work on the second screen even it is my pc monitor not the cintiq. On the main monitor substance works perfectly in every case.
I am a little problem with textureset settings in substance painter, I have changed the dimensions of a helmet texture set to what i am hoping is 2048 wide by 1024 high, but as their is not even a "w" and "h" and as the texture or canvas in the 2d view is still a square when I had thought it would change into a rectangle and their are still rectangle pixels on the helmet in 3d view.
When I import my model (.fbx) to draw a texture in the substance painter and export it to the .gltf format, I find that the metal I paint is gone and replaced by the shiny black, and then when I put the exported model in the three.js/examples/webgl_load_gltf.html case, I found that my model was dark and needed to be added a directLight can only see a point, the effect is not very good, but the case of importing the painter painter does not have any problems.