@Peter Horsbøll Møller? Peter, we did see some strange thematic template behavior when Pro 17.0 shipped - I believe the presence of the 17.0 beta was a factor...
The biggest problem we found was the inability to utilize custom thematic templates, created in previous versions - the custom templates did not appear in the 17.0 thematic dialog after being copied to the correct folder...
Some users also found that the 17.0 theme dialog showed only numbered thematics and not the expected thematic template names.
Those issues (and others) should be resolved in the Pro 17.0.1 patch/upgrade.
We recommend users patch to 17.0.1 and see if their thematic issues are resolved.
Note: Please read the Pro 17.0.1 Release Notes before patching, as this is a brand new global installer and the process actually uninstalls Pro 17.0 and installs 17.0.1.
http://reference1.mapinfo.com/software/mapinfo_pro/english/17.0.1/MapInfoProReleaseNotes.pdf