Hi,
Using v19.5a, win10, nvidia 940M
For "DialogFreeze004 external JPG MAT MDL ACT CHO.prj" that freeze without panel.
For "Delete.prj" it open, but without "vase" model.
For "VaseSlide.cho", it's ok, a panel ask for the "vase.mdl". So I choose "vaseX.mdl", it dont' freeze, and open the scene with the vase.
After If you close the project (not AM). You can open "DialogFreeze004 external JPG MAT MDL ACT CHO.prj" witout problem. (as if it had remembered the path of the folder where the files are located)
On v15, not this problem, a panel dialog ask for the "vase.mdl"
This is a problem that I have already encountered, when a file searches for an image for which it cannot find the correct path, it freezes.
Hope this can help