I can find no mention of the error we are occasionally seeing. We've had Social Customer Service setup for years and in a few different orgs without issue.
The error message we are getting is "error.network.private_messaging_blocked". When I first saw it I assumed this particular FB user has revoked permission for apps to send them private messages, but we've seen it for multiple users now in the space of a few days. It's only happening on one of our social accounts so far.
I've raised a case with Salesforce to get some clarity on the issue and will update here when I get a response.
Anyone else having the same issue, or has seen it before?