If Bamboo or another build system attempts to send a build status and fails for any reason, there is no retry mechanism and the old status remains indefinitely. This suggestion might fit better on the side of the producer of build statuses (and simply having them retry the send), but there may also be something Bitbucket Server can expose to help build status providers handle this in a more robust way (e.g. BBS could accept a status URL that it pings to pull updates rather than having them pushed).