While the Solstice Event continues in Pokémon GO, Gyms – the only way to gain coins without paying real money for them – will close worldwide on the 19th of June. This is part of a revamp to the system.
In preparation for some exciting new features, we’ll be temporarily disabling Gyms starting June 19. Stay tuned for more information.
— Pokémon GO (@PokemonGoApp) June 17, 2017
Don’t worry if you have a Pokémon sitting in a Gym – they’ll be returned to you when the Gyms are closed. A Niantic employee has been quoted that the closure will likely occur during business hours (PDT).
There’s no indication for how long this closure will last, nor has there been any leaks regarding how the new Gym system will work when it returns. We can expect a new update to supply the necessary data for the new Gym system.