We have found and fixed this issue. We will continue to monitor for further issues for the next few hours.
Posted Oct 29, 2018 - 19:19 UTC
We have confirmed that issue is localized to Bitbucket repositories that use the legacy oAuth tokens for authentication. We are continuing to look for a solution. In the mean time, the issue can be resolved by going to Settings > Repository and configuring a new private key for authentication.