I have installed the latest version and if I launch as part of the installation, everything functions perfectly. Once I close it and re-open, thereafter it no longer has the 3D portion of the display - so no models are showing. Looking at the logs shows many lines like these:
2019-06-17 10:50:24,688 - DEBUG - [MainThread] cura.Machines.QualityManager.initialize [136]: Lookup tables updated.
2019-06-17 10:50:24,707 - DEBUG - [MainThread] UM.Qt.QtRenderer._initialize [181]: Support for Vertex Array Objects: True
2019-06-17 10:50:24,709 - CRITICAL - [MainThread] cura.CrashHandler.__init__ [61]: An uncaught error has occurred!
2019-06-17 10:50:24,712 - CRITICAL - [MainThread] cura.CrashHandler.__init__ [64]: Traceback (most recent call last):
2019-06-17 10:50:24,714 - CRITICAL - [MainThread] cura.CrashHandler.__init__ [64]: File "X:\4.1\build\inst\lib\python3.5\site-packages\UM\Qt\Bindings\MainWindow.py", line 218, in _render
2019-06-17 10:50:24,716 - CRITICAL - [MainThread] cura.CrashHandler.__init__ [64]: File "X:\4.1\build\inst\lib\python3.5\site-packages\UM\Qt\QtRenderer.py", line 118, in beginRendering
2019-06-17 10:50:24,718 - CRITICAL - [MainThread] cura.CrashHandler.__init__ [64]: File "X:\4.1\build\inst\lib\python3.5\site-packages\UM\Qt\QtRenderer.py", line 183, in _initialize
2019-06-17 10:50:24,720 - CRITICAL - [MainThread] cura.CrashHandler.__init__ [64]: File "X:\4.1\build\inst\lib\python3.5\site-packages\UM\View\GL\OpenGL.py", line 45, in __init__
2019-06-17 10:50:24,722 - CRITICAL - [MainThread] cura.CrashHandler.__init__ [64]: RuntimeError: Try to create singleton 'OpenGL' more than once
This is on a Windows 10 Pro with a NVIDIA 750. All works great if launched as part of the install but fails after subsequent launches. I've tried compatibility settings based on similar (but not identical) situations from the forums with no luck.