It appears that the site editor for Open Data V1.10 has been closed a week early?
Can someone confirm
We have not disabled editing for 1.10 sites. Please submit a ticket with support so we can track this properly.
You might want to check again - I raised a call with Esri UK today and they can replicate the problem there is an Internal Server Error 500 when inspecting the save button on Open Data 1.10 site editor
This is a bug that we are currently fixing - we have not flipped the switch for disabling editing.
Thanks Courtney for looking into it and working on it