JCH is known (at least for me) to rule the web as they are the only extension installed. When there are issues with extensions / plugins first question i ask is always is JCH Optimize installed: if yes, turn it off and see if that fixes the issue.
JCH Optimize breaks the iframe by removing the src attribute. by doing that the iFrame cannot load because there is nothing to load. When the broken iFrame comes into to view, JCH repairs the iFrame by re-adding the src attribute.
Long ago, that was a very tricky lazy loading implementation. Since then the world has moved on and lazy loading is now a browser standard. You can simply add the loading="lazy" attribute to any iFrame and the browser will handle it as such.
Maybe I can have ochFitVids set the loading='lazy' element on iFrames it finds and processes. That way you have optimum sized videos AND lay loading conform latest standards (which Google likes as this is a standard I believe they introduced, or took part in).