That happened to me before, and there were a couple of things I tried which helped, but first consider if it might be something not worth troubling over- it could be that the URL it tried to index was already indexed, or it was an unpublished hub, or a bug on your page, or something of that nature.
Sometimes, that problem will go away without you having to do anything, programs have hiccups, and google bots are no different.
Another solution to try would be to resubmit your sitemap, under sitemaps on your dashboard.
And another, if you can determine which hub isn't being indexed, is to submit an RSS feed which includes the missing hub, and that often helps.
Good luck, and let us know what happens.