I find a walk around myself: Settings->Scalability->Preview Rendering Level, change from the previous “Shader Model 4” to “High End Mobile / Meta → iOS Metal Preview” will make the display OK. (The first time takes really really long time, maybe up to 10 minutes, as if the editor is frozen.)
The problem is the option cannot be saved. Every time I open the editor, I need to reset it, though latter change of the option takes only a few seconds.