As I reported previously for 5.5.1, 5.5.2 STILL does not handle 404 errors properly when using a custom 404 page per the directions at https://www.joomshaper.com/blog/create-a-custom-joomla-404-page-with-sp-page-builder.
In 5.5.1, when I insert the code suggested to redirect to my custom error page at https://www.certifiedinfosec.com/index.php?option=com_sppagebuilder&view=page&id=107, it showed the dynamic content error previusly reported.
Now in 5.5.2, it no longer shows the dynamic content error. With no special error code inserted, it tries to show my 404 error page, but it shows the mobile version and desktop version both instead of properly handling it for responsive display . See https://www.certifiedinfosec.com/kjhg. This is what I was accusomted to seeing without the custom 404 page guidance from https://www.joomshaper.com/blog/create-a-custom-joomla-404-page-with-sp-page-builder.
If I add the error.php modification using SPPB 5.5.2, however, I no longer get the dynamic content error as with 5.5.1, but now get a hot mess of images and actual error coding displayed. What a mess. I took the custom page code back out of the error.php for now until this gets fixed.