.. but it was right? That MNTP was showing it’s children and now they’ve all disappeared. Well it’s probably due to a node that would show in the picker not being published. It may even have a URL of ‘#’. Well you can find that node by running a query up against the Umbraco DB.
SELECT * FROM umbracoNode FULL OUTER JOIN cmsContentXml on umbracoNode.id = cmsContentXml.nodeid WHERE umbracoNode.parentId = {Id of parent node in picker tree}
What you may see in the results is a node that doesn’t contain any XML, this may be because it’s un-published or this could be the offender(s). Usually a republish of those nodes is enough to sort things out, if not there may be a custom datatype on there throwing exceptions.