The issue is not reproducible from their in-house environment, however the root cause was found from the investigation package that was provided.
An official fix is due to be released for the Sandcastle module and will come via Automatic Updates. No download and installation is needed.
The exact date this November is not known yet.
We can park this case for now until that official fix is released.
Please send me a screenshot of your DDAN update page https://DDAN/pages/active_update.php so we can monitor your version. From the investigation package you sent the version of Sandcastle is 6.0.1502.