When a federated user interact with a MUC room, that interaction should be processed. In this example, a remote user asks for a vcard of a MUC service (to get its avatar). There's no reason why this shouldn't be possible. Other types of stanza has also been observed to fail in a similar manner (“Cannot process X of remote users”).
This problem seems to occur only on an Openfire domain that uses clustering.
This is potentially a duplicate of it might relate to the federated user not being connected to the right cluster node.
We’re still seeing this occurring, even after has been deployed. Doesn’t seem to be a duplicate.
My hypothesis is that a federated user is not consistently “on one cluster node”, causing its representation by either LocalMucUser or RemoteMucUserto not be consistent, and therefor, incorrect. Perhaps this occurs when a federated domain re-establishes its s2s connection to a different cluster node.