Seems to exist now again in 2019.1.2f1. I only have one inspector opened, relaunched Unity twice, and have defaulted to the 4-way layout. I do have VegetationStudioPro installed with all of the Packages it requires. When I launch a Project without Vegetation Studio Pro, it works. I know, I know, you may be saying its their bug. But... Its the Unity Inspector that is failing to work properly. Somehow it is letting VegPro say there are two inspectors open when there are not. Any ideas?