@mc .... I've had my host look at possible causes and they came up with zip (see below).

So it appears something likely within the CEON code is not submitting the uri mapping correctly to the server (if at all) such that the server can recognize it, (guessing here - possibly in a corrupted format?) - regardless something is stopping the uri mapping from uploading when update is clicked in product_update HOWEVER only for new products since the new site was built (copied over) - possibly a bad ftp transfer of a crucial file in CEON? (grabbing at straws again). I can go into existing products and alter the existing uri mapping and the product still resolves - so it tends away from simply the update_product button.

I need to add some new products so may end up doing so by un-ticking the auto generate button in product creation and when the problem has been found I can go back and tick it and update - I hate doing this sort of thing as it screws things up with Google Search.

Hopefully you will come up with a fix soonish - I will keep trying different things my end.

Importantly ... can I re-install CEON without losing existing mapping data? .... if so then that may be a good step - if it does lose the existing data then not so good.

cheers,
Mike

from my host:

I have contacted a Senior Technician to overlook your query and we both can confirm that your rewrite conditions will not have an effect to your 404 issue.
I would also like to mention that this cPanel service is also on the same server as the domain dazzlersharmonynecklace.com.

Both of these domains are being resolved from the following shared IP address:

------------------- A/AAAA record(s) -------------
103.27.34.7 >> r131.syd3.hostingplatform.net.au.

While your error logs have also not provided any issued related to the permissions of this website specifically, I suggest running our Permissions fixer tool which will default your files permissions to 755 and 644 respectively; this will also eliminate the concern of the incorrect permissions within this specific cPanel account.
This can be done via the following:

Log into VIPControl >> Web Hosting >> Manage >> List Accounts >> Manage >> Permission Fixer