This can happen if the host setting is not visible somehow. We’ve seen a similar case of this recently, you may find useful clues in this other thread. If not, please let us know how the host is configured.
I’m not sure that means exactly, can you please clarify? The content of the sonar-project.properties file with private details masked could be useful too.
I’d say very very odd. Do you have a rough idea of the percentage of such failure over successes?