Thanks Justin,

Glad I spotted this article this morning. I ran into this issue with jQuery straight away on one of my first updates. A simple script, enqueued in my child theme, to set my header logo to inverse as the page scrolls, specifically for Firefox which has its own notions on these matters regarding the css option that other browsers seem to like. Such a simple thing meant some elements on certain pages just did not want to load. Initially I though it was some sort of clash between the new lazy load built in and some other plugin that was already doing this.

When I activated Enable jQuery Migrate Helper all was well again but by all accounts it looks like there will be some work to be done or not. Not completely sure yet???