At first, it was difficult to confirm if it was truly a bug since relatively few people got affected, but Blizzard has admitted in a statement that the issue exists. The developer promises fixing the bug is the team's priority at the moment, but it can't say when it can roll out a fix. It assures everyone, however, that it will lift affected players' seasonal bans so they don't contribute to the possibility of a permaban and will also restore people's skill ratings. It'll obviously be a hassle to get the issue fixed if it ends up affecting you, but at least you won't have to worry about not being able to play this season at all.
"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."