See http://xtools-dev.wmflabs.org/articleinfo/en.wikipedia.org/Hanksy

It seems this is another case where PHP very graciously suppresses the error in production. The "isRevert()" logic just returns false, which does mean for some pages the data will be off a tad bit, but at least it doesn't blow up.

To explain the issue: With T170888 the automated edits detection system was reworked so that it can be configured on a per-wiki basis. For the actual AutoEdits tool it's using code in User.php that properly references the requested project, but in ArticleInfo we're using the soon-to-be-depracated AutoEditsHelper, which does not reference the project. This is what's causing all of these Undefined index errors.