Return a WP_REST_Response or WP_Error object from your callback when using the R

From our logs:

{
	"function": "wp_send_json",
	"message": "Return a WP_REST_Response or WP_Error object from your callback when using the REST API.",
	"version": "5.5.0",
	"exception": "
        #0 \/path\/to\/public_html\/wp-includes\/functions.php(4107): _doing_it_wrong('wp_send_json', 'Return a WP_RES...', '5.5.0')
        #1 \/path\/to\/public_html\/wp-includes\/functions.php(4151): wp_send_json(Array, NULL, 0)
        #2 \/path\/to\/public_html\/wp-content\/plugins\/sg-cachepress\/core\/Rest\/Rest_Helper_Options.php(142): wp_send_json_success(Array)
        #3 \/path\/to\/public_html\/wp-includes\/rest-api\/class-wp-rest-server.php(1139): SiteGround_Optimizer\\Rest\\Rest_Helper_Options->fetch_options(Object(WP_REST_Request))
        #4 \/path\/to\/public_html\/wp-includes\/rest-api\/class-wp-rest-server.php(985): WP_REST_Server->respond_to_request(Object(WP_REST_Request), '\/siteground-opt...', Array, NULL)
        #5 \/path\/to\/public_html\/wp-includes\/rest-api\/class-wp-rest-server.php(412): WP_REST_Server->dispatch(Object(WP_REST_Request))
        #6 \/path\/to\/public_html\/wp-includes\/rest-api.php(354): WP_REST_Server->serve_request('\/siteground-opt...')
        #7 \/path\/to\/public_html\/wp-includes\/class-wp-hook.php(292): rest_api_loaded(Object(WP))
        #8 \/path\/to\/public_html\/wp-includes\/class-wp-hook.php(316): WP_Hook->apply_filters(NULL, Array)
        #9 \/path\/to\/public_html\/wp-includes\/plugin.php(551): WP_Hook->do_action(Array)
        #10 \/path\/to\/public_html\/wp-includes\/class-wp.php(388): do_action_ref_array('parse_request', Array)
        #11 \/path\/to\/public_html\/wp-includes\/class-wp.php(750): WP->parse_request('')
        #12 \/path\/to\/public_html\/wp-includes\/functions.php(1291): WP->main('')
        #13 \/path\/to\/public_html\/wp-blog-header.php(16): wp()
        #14 \/path\/to\/public_html\/index.php(17): require('\/home\/customer\/...')
        #15 {main}
    "
}

Twice in quick succession, today, no occurrence in previous 12 days.

PHP 7.4.2. WordPress 5.7.2. SG Optimizer 5.8.0.