When saving SketchUp documents, on the server or local desktop or documents folder. SketchUp will stop responding for about 5 minutes while saving and then eventually saves.
I have uninstalled the SketchUp 2018 and all other versions and reinstalled only 2018 but it still does the same thing.
if disabling the thumbnail option helps it’s likely that the used graphics card resp. driver is involved in the issue (OpenGL).
Ensure running the latest driver version (see “Windows+R > dxdiag > Display”) as well as running SketchUp on the dedicated nVidia GeForce and not on an maybe integrated intel HD: