Thread:Project:Support desk/Fatal error: cannot access private property/reply (4)

I downloaded and upgraded to a fresh copy of 1.23.3. Copied over my LocalSettings, logo and favicon files, and 3 extensions I use -- BreadCrumbs, MobileFrontend, and HipchatNotifications. Upgrade went fine, no issues at all viewing pages, I go to upload a file... exact same error.

I feel like this must be external to MediaWiki, but don't know how to debug PHP in this instance.