Ah, “good”. Having same problem, so i’ll bookmark this for updates… 
(But i’m on Windows, not on a Mac… 
)
Edit, because i’n not sure about double-posts here
@kaxline and @jimmylee for me a re-install of Expo on Windows fixed it. Maybe it had something todo with the last security update from Microsoft. 
Because it was working all the time but on the next day i had this problem.