User blog comment:Kirkburn/Technical Update: July 18, 2016/@comment-24473195-20160719142323

We have previously fixed an issue that caused the "Non-portable infoboxes" Insights list to report non-existent pages outside the template namespace.

I guess you need bigger shoes to crush this bug, it keeps coming back with a vengence, see (http://fairytail.wikia.com/wiki/Special:Insights/nonportableinfoboxes), http://fairytail.wikia.com/wiki/User:Gauzz_Rifle/FanonInfoboxFT?insights=nonportableinfoboxes. Although it could possibly be due to caching.