WMS imagery service not displaying in ArcGIS Online new viewer

We did notice such issues sporadically on AGOL as well - sometimes it works on old viewer, but not on the old, sometimes the other way around.
We have tried troubleshooting with them as well, but with no success and the comment you provided (i.e. Javascript) seems the issue is on their side.
Sentinel Hub OGC APIs are in line with standard and they should work everywhere.

If you can put us in contact with your AGOL support we can possibly troubleshoot further.

Thanks so much for getting back to me. I have an open support case with ESRI, not sure the best way to get you all in touch with them. If possible, please email me  so I can potentially provide them a way for you both to troubleshoot this issue. I have some logs from the developer console that may help as well.

So I spoke to an ESRI support analyst regarding this issue and we resolved this by removing the domain https://services.sentinel-hub.com from the list of Trusted Servers in the security settings in our AGOL account. Removing that resolved the issue and the Sentinel imagery services are now correctly displaying in the old AGOL viewer, the new AGOL viewer, and in ArcGIS Pro. Hope this is helpful to anyone else running into this issue but doing that seems to have resolved this issue for now.