Hi Peter,
I will share how this has converted incorrectly for you to our dev team for further investigation, as it should have converted over correctly on upgrade.
We are aware of some limitations in v4 for users who have previously used optional stylesheets and are looking to address this in our v4.1 release.
Do take a look at our latest topic in our Inside Xibo category which further explains our planned improvements for 4.1: Key improvements for 4.1
In the meantime you could create an XML template with your customers required formatting and styling and then upload to their CMS to be used with their RSS feed.
Further information on Templates can be found in our developer documentation: Templates - Widgets | Xibo Digital Signage