Since Dynamic Properties seem to be disabled by default in EPiServer CMS 9, you need to set this web.config (or was it episerver.config?) attribute:
... as already stated in the breaking changes, please see here for more breaking changes http://world.episerver.com/documentation/Items/Upgrading/EPiServer-CMS/9/Breaking-changes/
Since Dynamic Properties seem to be disabled by default in EPiServer CMS 9, you need to set this web.config (or was it episerver.config?) attribute: