Yesterday there was an issue with Overwatch's D.Va that meant she had to be taken offline in all regions, however, you may not have even noticed it happened, as she was only offline for a few hours. Regardless, she's back now, as announced by Blizzard on Twitter.
While Blizzard itself didn't specify what this issue was, a commenter by the name of Snuggle said that there was a bug which meant she could restart competitive matches, meaning people were exploiting it to avoid losing skill rating.
Did you encounter this bug?