Just to clarify, the “Unexpected Server Error” message is not likely to be associated with any current maintenance schedule. Details from Blizzard Customer Service here:
Hello everyone,
Thank you for reporting this. I was able to confirm that our Overwatch team is aware of this “Unexpected Server Error” which is only affecting certain accounts and they are working on getting it resolved as quickly as possible.
Due to the complexity of the problem this may take several days or more to be resolved. I’m afraid we don’t have a hard ETA that we can provide, but rest assured they are working on getting each account fixed up.
Customer Support is not able to manually fix these accounts, so we ask that you don’t submit tickets about these, however you can continue to keep trying to log in every so often to check if the account is fixed up.
Apologies for the interruption though and we appreciate your patience while the issue is being worked on. If we hear of any updates from the Overwatch team we’ll be sure to post in this thread.