Jetpack Classic Slideshow broken layout after update

I use the classic Slideshow with CSS mods to add a white background and remove or restyle the captions. The slideshows are used in a large number of posts across multiple sites, and the latest update appears to have corrupted the display of all of them.

The latest version does not resize images to fit the window, CSS selectors have been changed, so the background (previously white) is now black, and the captions do not render as they should.

Converting these to Gutenberg has not been possible because:

(1) the Gutenberg slideshow block does not render images and captions in the same way.
(2) There is still an (3-4 year old outstanding) Gutenberg bug where ‘convert to blocks’ does not correctly convert Jetpack slideshows and galleries
(2) Tracking down all the slideshows over alarge number of sites and posts is just not practical.

Something needs to be done to ensure backward compatibility.

The page I need help with: [log in to see the link]