On my project I get this error when I click on a GUI element in the inspector and the right panel disappears.
I am using XMLLoader to load my GUI elements and I cannot load an XML on the PG to test. I still did an online demo of the problem. I put the inspector.bundle.max.babylon
Load the game, wait until the character is fully loaded. Then select the GUI element in the left panel of the inspector (the right panel disappears)
Not in fact, it is not before babylon.js that the inspector should be referenced, but before babylon.gui.
Conclusion for this to work properly, the order of referencing really changes things.
This should be indicated in the doc I think to avoid that others this mistake when adding the inspector. It must be after the GUI which is also after Babylon.