Smush CDN making site down

If I enable Smush CDN my Server Load goes up and my server return 503. When I disable the CDN the site be back to normal, on my logs I see:

[Wed Nov 20 16:20:21.324916 2019] [lsapi:notice] [pid 1968040:tid 47805339014912] [client 185.53.58.3:41056] [host n+++++++++.co.uk] Backend log: PHP Warning: getimagesize(https://n-++++++++.co.uk/wp-content/uploads/2019/01/lawyer.png): failed to open stream: HTTP request failed! HTTP/1.1 503 Service Unavailablern in /home/+++++++++/public_html/wp-content/plugins/wp-smush-pro/core/modules/class-cdn.php on line 1144n

The reported images are 404 images, but I can’t see those images being loaded on the front end. Can you help me?