Hi @Ronnie09
I faced similar issue in classic ui where I noticed that in ootb file libs/cq/ui/widgets/source/widgets/wcm/EditBase.Listeners.js there was a logic related to checking selector with was failing essentially adding a"..html" at the end of the post call.
Similarly for your core.js where it is failing can you try to troubleshoot/debug and find what file the issue is happening and why? It could be another issue and not same, but just wanted to share if that helps and a similar approach can help. Please share the part where it is failing in core.js.