Google has ceased to support them. They were a nice element in blog posts.

I will be replacing them slowly over the next few weeks.

Update:

I have edited the affected pages; which were all prior to 2016.

There is no need to go into the technical issues, you will find a number of tech discussions on this topic beginning in 2016. Suffice to say that in 2016, Google withdrew the excellent Picassa photos platform from the market. To Google’s credit, they supported the code that worked with Picassa for a very long time; and the photos were incorporated into Google Photos. As of January 2019, all support for the old Picassa code was withdrawn and the slide shows ceased to function.

I’m sorry about this development, the blog pages prior to 2016 were really built around the slide shows, they eliminated the need for much editorial content. I found that I had to redo a couple of pages, they would have been unfathomable otherwise.

Finally, if you look, all photo posts can be viewed as a slideshow once the OneDrive or Google Photos page is loaded.