@patl I imagine all the issues are as per the link posted above and its simply that there are only 3 shaders in the directory specified, and the next/previous feature doesnt traverse sub directories.
So you could get round it by either moving some shaders around, setting your paths manually to look at a different dir or just manually setting a system specific config to load the one you want.
Maybe I’m in a minority but I tend to find one I like and stick with it rather than scroll through loads.
Have you tried davej shader?