In addition to the SEO: Not Available I am also getting a front page error with the Rank Math activated.
I installed the Health Check plugin and went through enabling each plugin and had no problems with the site except for the Rank Math. In addition, I installed the 2017 WordPress theme and used the Health Check plugin to verify that the problem is with Rank Math - Not the mytheme shop themes. No Issues show up in that section of the Health Check dialog.
Finally, I turned off the Heath Check and the deactivated ALL the plugins. The site worked. When I just activated the Rank Math the front page broke. I then activated all the other plugins and the site worked. Finally, I activated the Rank Math plugin one last time and the front page broke and the SEO: Not Available showed up again. I currently have the Rank Math deactivated.
I've been using MyThemeShop since the beginning and this is the first time I've had an issue with one of your plugins.