Changes that merely change the order of sitelinks (and maybe others) lead to the dispatcher choking and not moving forward. Here's the analysis by Katie:

After investigating on toollabs with the copy of the wikidata database there, it looks like change id 55754448 is the odd one:

http://dpaste.com/1300944/

http://www.wikidata.org/w/index.php?title=Q13360583&diff=57098298&oldid=54370606

For that change, DiffChange->getDiff() (and getSiteLinkDiff) are returning a DiffOpChange object. For all other changes, it is an ItemDiff object.

The site link diff involves changing the order of the site links in the array, but otherwise a null change for site links:

Diff\DiffOpChange::__set_state(array(

 'newValue' => 
array (
  'svwiki' => 'Projekt 661 Antjar',
  'dewiki' => 'Papa-Klasse',
  'frwiki' => 'Classe Papa',
  'cswiki' => 'Projekt 661',
),
 'oldValue' => 
array (
  'cswiki' => 'Projekt 661',
  'dewiki' => 'Papa-Klasse',
  'frwiki' => 'Classe Papa',
  'svwiki' => 'Projekt 661 Antjar',
),

))

Version: unspecified
Severity: critical