[Smush Pro] Smush CDN fails to load resources

I keep getting errors related to Smush CDN that fails to load images:
[Error] Failed to load resource: the server responded with a status of 504 () (OKT-Albert-1024_1.jpg, line 0)
[Error] Failed to load resource: the server responded with a status of 504 () (Niemeläinen-1024_2-e1565948598963-400×284.jpg, line 0)
[Error] Failed to load resource: the server responded with a status of 504 () (Vihdinpuisto-1024_1.jpg, line 0)
[Error] Failed to load resource: the server responded with a status of 504 () (Kankareen-Paalutus-1024_1.jpg, line 0)
[Error] Failed to load resource: the server responded with a status of 504 () (Niskaparkki-lattialämmitys-e1565949646146-400×284.jpg, line 0)

I have the same issue on another website too. Can you please help? The support access is enabled, but I will disable the Smush CDN for now, since the website is live.