e.g. https://wikiapiary.com/wiki/Wikipedia_(en): click "General" and you'll see most of the fields are blank, the "MediaWiki Version" field has a SMW error, and there's a big mess of code at the bottom. This is caused by nested {} in the pageviewservice-supported-metrics parameter on [Website]/General (e.g. for "Wikipedia (en)", the value is {u'siteviews': {u'uniques': u'', u'pageviews': u''}, u'mostviewed': {u'pageviews': u''}, u'pageviews': {u'pageviews': u''}}; note the }} at the end).

In addition to pageviewservice-supported-metrics, this could potentially also affect the readinglists-config, galleryoptions, linter, imagelimits, wmf-config, and magiclinks parameters, so any fix should also apply to them (if possible, it might be best to just apply it to all parameters).