"Failed to initialize: The Sims™ 4 is running."

I can't start a game in The Sims 4. Instead of starting the game, I get a window saying the game is running. This problem can last for days, then suddenly let you play, or a day or two later, it reoccurs.
I've reinstalled the game, the EA platform, and serviced my Mac, and the problem persists.
I've had this problem since the end of January.