oh, i have misread this topic completely lol, too many things going on at once.
Mesh editor has the black screen. right, lets solve this one.
and any changes you make (if you change the scale, for example), are not reflected in the model back in the editor.
To get what you see in the mesh editor back in the scene, press the reload sceneEntity button on the main toolbar or RMB + context menu in the main editor. This is required because, the mesh you edit in the mesh editor is a temporary object so any deforms on skeletons and animations don't break the character in the scene and make all the arms go all squiffy lol
Then when saving, it overwrites the mesh you have in the scene, but it requires a refresh for changes to take effect.
There are plans to improve this, so the editor autodetects changes and offers to refresh instead for you.
It would be good to see this black screen in the mesh editor though.
Perhaps the ground plane was turned off leaving the black background, this can be turned on or off on the mesh editor toolbar.