Missing hub initiative page

[DataOfficer]

I have gone to edit one of our Hub Premium initiative pages and it is missing with the following behaviour:

• If I open the initiative in edit mode the page is missing from the list of pages.
• If I try using the direct URL (using a custom domain) I get the error: 404 So sorry. We looked everywhere and just can't seem to find what you were looking for.
• If I look in my ArcGIS Online Contents, the page is still there, but clicking on Configure App results in the same error as above.
• If I use the direct URL containing the item ID (e.g. customdomain.org/edit?pageId=1234abcd) the page opens. However, if I try and publish the draft I get the error Publish failed. Also, the left customisation/editing pane is displaying weirdly as shown below.

How can I recover this page?