In Chrome OS 11294.0.0 (and possibly earlier versions), first time I've seen this but it may be a startup race condition so worth taking a look at.  When starting Crostini through Chrome we ended up with this error:

2018-11-24T23:27:15.566064-08:00 ERR vm_concierge[31853]: Failed to call method: org.chromium.Seneschal.StartServer: object_path= /org/chromium/Seneschal: org.freedesktop.DBus.Error.ServiceUnknown: The name org.chromium.Seneschal was not provided by any .service files
2018-11-24T23:27:15.566091-08:00 ERR vm_concierge[31853]: Failed to send StartServer message to seneschal service

Full logs are here:

https://stainless.corp.google.com/browse/chromeos-autotest-results/260836789-chromeos-test/