OOPS this one isn't built using the latest version it's the same one as the music site,

OK so I am assuming that the doggy website https://www.lmstest.net/index.html is the one that Philip is having problems with, because there are still some pages flagged as "Under Construction"
It's the latest version and using Bootstrap 4.

I had the same thing happen and had to recreate an entire website. It's tedious, especially working with a 32 bit system. But, if you have the exported files or html for your pages or if your site is working, use it as a resource to recreate it. It will take time. But it is possible to recreate it.

I'm glad to know I'm not the only one with these issues ~

I have gotten into the habit of using the save function and creating backup rsd files, like site.rsd, site-1.rsd. I copy those to a backup drive so I have something recent to rebuild off. I also save the current rsd file to the website server.