Confirmed as well… Can’t add/edit Groups. Using Classic Editor as well as disabling Gutenberg with…
// Disable Gutenberg
if (version_compare($GLOBALS['wp_version'], '5.0-beta', '>')) {
// WP > 5 beta
add_filter('use_block_editor_for_post_type', '__return_false', 100);
} else {
// WP < 5 beta
add_filter('gutenberg_can_edit_post_type', '__return_false');
}
*** as well as other Gutenberg disabled snippets
