I’m using 5.8.0-beta3 & WP 5.0 and experiencing this same issue.
I tried the fix suggested by @elliot above, but the plugin file structure seems a bit different and I cannot find that line of code.
I have copied the example (for testimonials) exactly. I am able to select the location of “Testimonial” when I add the field group, but “Testimonial” does not appear in the editor.
I’m happy to roll back to an earlier beta, but wanted to see if anyone else was having this issue with beta 3 & WP 5.0.
