Did this happen after an upgrade from NC 9 to 10? There is nothing in your logfiles I suppose? Can you delete and add the federated sharing?
If you can’t find anything obvious, it may be worth waiting a few days until version 10.0.1 finally gets released (RC1 is currently tested: Help testing the 9.0.54RC1 and 10.0.1RC1). Your issue is perhaps fixed before you dive in a longer debugging session.