I`ve had this issue since Corona v 10 and its frustrating that not Chaos nor Autodesk does anything about it. Just switch to Slate editor, it doesn`t crash there, but I hate the slate editor and it`s frustrating to work, copy, paste materials and maps in there, cant drag things from diffuse map to reflection or bump, you have to connect it and then you get a jumbled mess of wires and tabs. Jeez.
I`m not sure why compact material editor does this but it`s troubling that they can`t solve it. It crashed when trying to load a corona brick material and a black metal material in a multi-map. Not rocket science yet it crashes max. Luckily it saves a recovery file.