I could confirm the issue on your shared site but i have tested it on my test site and it’s working fine for me using latest version of Sparkling theme.
Would you mind if i log in to your site and do some troubleshooting? If this is ok then could you please share me your site log in details privately by checking the option “Set as private reply” when replying to this topic?
I logged in to your site and just unchecked & saved the theme option “Show post excerpts?” and again checked & saved which made the read more button to display.
Could you please check it and let me know whether it is working fine for you now?