Update: According to Blizzard, D.Va is now available to play again in all regions:
Thanks for your patience while we addressed this issue. D.Va is now enabled in all regions on all platforms.
— BlizzardCS (@BlizzardCS) April 28, 2017
Blizzard has not given a specific reason for the emergency maintenance, but players are speculating that it’s connected to a recent spate of server disconnection bugs that appeared to stem from the character.
Blizzard has removed D.Va from the Overwatch lineup temporarily in order to fix a bug.