Hey!
After 6 months we are going to remove a compatibility layer from the Wikibase source code that may affect your Wikibase installation if it uses custom entity types. If your LocalSettings.php contains something like
$wgWBRepoSettings['entityNamespaces'][CONTENT_MODEL_WIKIBASE_ITEM] = WB_NS_ITEM;
or
$wgWBRepoSettings['entityNamespaces']['wikibase-item'] = WB_NS_ITEM;
you should change it to
$wgWBRepoSettings['entityNamespaces']['item'] = WB_NS_ITEM;
In other words: The entityNamespaces[*] setting required content model IDs like "wikibase-item" before, but requires entity types like "item" now. That's all.
Best Thiemo
[*] https://phabricator.wikimedia.org/diffusion/EWBA/browse/master/docs/options....