After running GLTF successfully & looking at their source, they were not passing a desgraph in to_mesh(). Checked API, there are now no args to to_mesh().

I work on the exporter for BabylonJS. It is (or was fully updated for 2.80). I refreshed my Blender yesterday ( windows 64 bit), and I get the same issue. Do not think this should be closed unless the api has changed for getting a depsgraph someplace other than the context.