Raids have been in Pokémon GO since July 2017. Since then, players have noticed some bugs that make Raids unfair and raiding frustrating. Niantic has confirmed a few of these bugs.
Update September 1, 2017: The “Last Ball” bug has now been fixed
Original report:
Raids have only recently been introduced in Pokémon GO. Here, trainers team up to fight a particularly strong Pokémon in an arena. When a large egg with a countdown appears above an arena, a Raid Boss will soon be here. This is a Pokémon with extremely high CP values and various difficulty levels.
Trainers get the chance to catch the Raid Boss if they defeat it.
With the big GO event, Niantic also introduced legendary Raids. Here, trainers face legendary Pokémon like Lugia or Articuno and can also catch them if they defeat them.

These bugs occur in Raid battles in Pokémon GO
Catching Raid Bosses works differently than catching regular Pokémon. They are captured using special Premier Balls that can only be obtained during the Raid. The Raid Bosses and legendary Pokémon can only be caught using the Premier Balls!
The number of Premier Balls a trainer receives after a Raid battle depends on various statistics, such as the damage dealt by an individual trainer or the average damage of their team.

Those who receive only a small number of Premier Balls already have it hard to catch the extremely strong Raid Bosses. Hence, the following bugs are a real nuisance for many trainers.
- The Last Ball Bug: It is impossible to catch legendary Pokémon with the last Premier Ball. Thus, trainers have one ball less than they should. Niantic has officially confirmed this bug and has given trainers an extra ball for raiding since August 7. However, all trainers who participated in Raids before that were negatively affected.
- The Curveball Bug: If a trainer throws a Pokéball with a slight spin, they use the Curveball function. The ball flies in a semicircle towards the Pokémon and increases the catch rate. For unknown reasons, the game does not register every Curveball and the bonus fails to apply.
- The Team Control Bonus Bug: If their team controls the Raid arena, trainers should receive two extra balls after the battle. Niantic once stated in its customer service that this bonus is supposed to work differently. Only the trainers who have Pokémon defending in the Raid arena are actually supposed to receive the bonus. Sometimes trainers receive the bonus even if they have no Pokémon in the arena. Sometimes trainers with Pokémon in the arena receive the bonus.
- The Dodging Bug: If a Pokémon dodges an attack, it receives 75 percent less damage. However, the bug causes Pokémon to receive full damage, even if they successfully dodged. Especially the legendary Pokémon have attacks that can almost knock out a Pokémon in one hit. This makes it difficult for Pokémon to remain long enough in the Raid battle to earn bonus balls through extra damage.

Trainers need Raid Passes – one is free per day, the rest costs
These problems become particularly annoying when money is involved. Pokémon GO is free and mainly financed through premium sales in the in-game shop.
Those who want to participate in a Raid need a Raid Pass. Trainers can receive one Raid Pass for free once a day in an arena. There are also Premium Raid Passes. These are purchased in the in-game shop for 100 Pokécoins.
The standard and premium Raid Pass allow trainers to participate exactly once in a Raid.
Especially for the legendary Raids, trainers have spent a lot of money on premium passes – now the community is frustrated due to the bugs.
Niantic recently announced that Mewtwo will be catchable in an exclusive Raid will be available. Trainers must be invited to exclusive Raids. The invitation is only received if they have had a “recent” Raid in the arena where Mewtwo appears.
The community reacted with skepticism about whether the exclusive Raids will run smoothly when normal Raids already have problems and bugs.

Has any of these bugs cost you a legendary Pokémon?
These are particularly bad for villagers, who notoriously have far fewer arenas. At least, Niantic promises improvements here for the future.