UPDATE 09/27/2017: Jeff Kaplan has posted about the bug, stating the following:
We recently identified a bug that, in extremely rare cases, can cause players to lose their skill rating progress and receive a seasonal ban from Competitive Play without any prior penalties for leaving early or being kicked for inactivity. This bug is a high priority for our team, and we’re working on a fix to prevent further instances of it occurring as we speak.
In the meantime, we’ll be removing the seasonal ban for all players affected by this bug as well as restoring their skill rating. To date, this bug has impacted fewer than 200 accounts, but we’ll continue to monitor for additional occurrences and provide assistance until we can implement a permanent fix. We don’t have an ETA to share right now for when the fix will go live, but we’ll update this thread as soon more information becomes available.
We sincerely apologize for any inconvenience or frustration this bug has caused and are grateful for your patience and ongoing reports.
If you’re an avid Overwatch player, you’ve probably started playing competitive play. Not only are matches a little more serious, but you also get competitive rewards like sprays and golden weapons. Now, imagine that one day you try to log into your account, only to find that you’ve been banned from competitive play and lost all rewards. Furiously, you try to get to the bottom of the mystery, and the more digging you do, the more obvious it becomes: You’ve fallen victim to a bug.
This is a nightmare scenario, but Overwatch players are reporting it happened to them. Blizzard support also seems unable to help, as they cannot access the logs and dig deep into the facts of the matter. The result is that every time you play competitive, you could be rolling the dice on a season ban.
There are currently two active threads on the matter, one on /r/Overwatch and one on the Blizzard official forums, both compiled and created by the user Chromega.
Basically, it seems to happen if someone leaves right as the competitive match is loading or something. The match goes into a 'waiting for players' state, odd for competitive. The match tries to start, fails, and returns to 'waiting for players' with the same players and repeats. Folks who have seen this bug lose HUNDREDS of SR, and, most importantly, get season banned immediately, even with no prior disconnects. Seems like it affects everyone in the match, but I can't confirm.
I've found claims of several people who have hit this bug. The only real hard evidence I have are the Overbuff stats of some folks: https://www.dropbox.com/s/grju2y5ycw7hcvp/spicy_sr_drop.png?dl=0 or thishttps://www.dropbox.com/s/f1u23iib1hca9um/redandblack_ow_record.PNG?dl=0
Those stat changes should not be possible - even if you d/c, the incremental suspensions would prevent you from losing SR that fast.
Blizzard customer support says they can't fix it and asks you to post to the bug report forums to see if a dev will fix. But I've been posting every day for 3 weeks to no avail. My fiancee and I used to play together nearly every night since launch, and now we can't play comp, and that really blows (not really interested in QP). Really sucks that they're just beginning to implement a three-strikes-perma-ban system, so she's already starting with a strike.
Consider this a PSA, you may one day queue for a match that instantly bans you, and Blizzard will not help. Also consider it a plea, that if someone at Blizzard sees this, please unban the affected accounts, this is a really severe issue...
Other users are coming forward with similar tales, warning that they’ve been banned and you could be banned as well. The current theory is that the bug is caused by a user cancelling their search for a game, but being put into a game anyways, and thus automatically cancelling the match—which comes across as a mass disconnect.
Blizzard has yet to respond, but hopefully they implement a solution soon so players can get back to queueing for competitive with no fear in their hearts.