I'm trying to troubleshoot this with the domain owner, but cant really see beyond your 500 error. I suspect some issue with their CDN but could you check? some example url's:

https://images.weserv.nl/?url=www.arboss.nl%2Fwp-content%2Fuploads%2F2020%2F09%2Fhks-bfs-90.jpg
https://images.weserv.nl/?url=www.arboss.nl%2Fwp-content%2Fuploads%2F2020%2F12%2Fpuma-airtwist-black-low.jpg
https://images.weserv.nl/?url=www.arboss.nl%2Fwp-content%2Fuploads%2F2020%2F11%2FAlbatros-64.750-Impulse-AER55-Black-Blue-Low.jpg