Happened to me with my one and only Ho-oH raid but I wasn't aware of anyone backing out, at least not intentionally. It's possible someone got a network error though as there were a couple that were having GPS drift problems. Really sucky bug as we wasted a raid pass, revives and potions and got nothing to show for our efforts, plus it was solarbeam so it wrecked a lot of pokemon.
New raid error being reported on Silph Road
https://www.reddit.com/r/TheSilphRoad/comments/7h5858/how_to_avoid_the_raid_boss_catch_bug/
It appears if anyone leaves the raid fight, the players that remain and try to finish will be unable to complete and will not receive rewards and will not get a chance to catch. In addition, the battle button to start a new fight will disappear for 10 minutes after you error out with this bug.
- Start raids as soon as possible. Don't push them to the end of the raid timer.
- If one player backs out, all players need to back out.
- Use private groups so spoofers can't grief you.
Answers
Some reports that this also happens when the app crash during a raid. So not only intentionally backing out. I would add another recommendation, raid in small groups to minimize the chance of a crash, if someone crash during the raid and can't return before the kill, everyone should back out and start over.
Maybe this isn’t a “bug”.
Let’s say Niantic is trying to discourage the purposeful overpowering of a raid to beat down the boss quickly and then having many drop out to let a small group get better ball count. Take for instance an EX raid where 5 instinct, 10 valor and 15 mystic get passes at a mystic controlled gym. Let’s say that 10 mystic decide to raid with the 5 instinct and then back out when the boss is at 10%. As a result, the 5 instinct beat the boss and get all the damage balls, possibly getting 12 balls instead of 6 or 7. (This happened at the only EX raid I’ve done).
This new “bug” prevents that.
Of course it could just be another Niantic oops....