Pokémon GO might have added Legendary Pokemon to the game, but it’s still the same buggy game that crashes way too often. Sometimes, the game crashes at the worst possible moment… like when a player is right in the middle of a Legendary Raid.
If you can’t get back into the Raid before your group beats the Raid Boss, your game won’t always send you into the Bonus Challenge screen for your shot to catch the Legendary Pokémon. Instead, tapping on the gym will give you the option to start a new raid, which of course wipes out all the hard work you and your group already put into beating the Raid Boss the first time.
Just because you didn’t finish the raid doesn’t mean that you lost out on a chance to catch the Pokemon. In fact, the game should recognize that your account has a Bonus Challege and rewards coming to it. Players should NOT re-enter the raid battle, as it will cause the game to error out AND erase your chance to catch the Legendary Pokémon. Instead, players should either wait for the game to send you into the Bonus Challenge on its own or “force” the game to send you to the Bonus Challenge by spinning the photo disc of the gym you just battled in.
Please note that the latter option will often cause the game to crash (again), but you should be able to repeat the spin as many times as you need for a chance to catch the Pokémon.
Hopefully, Niantic will fix the crash issues before more players mistakenly miss out on their chance to catch a Legendary Pokémon. In the meantime, pass this fix along to any player having problems with the game!