User blog comment:DaNASCAT/Technical Update: September 26, 2016/@comment-5558012-20160926234646/@comment-126761-20160927110624

Unfortunately some underlying structural changes will mean that some custom personal JS (and CSS) will need updating. As much as we'd love to avoid affecting customizations, that isn't always possible.

(Edit: I've added a note about this to the main post as well.)