Your screen shot is too small to be readable,
That message indicates the cardio plugin is over riding the system tiddler $:/core/ui/ViewTemplate/subtitle
TiddlyWiki.com is a great place to go to find out what is the default (in many cases) although a fresh empty wiki the best
When I edit the subtitle tiddler on TiddlyWiki.com I get the message
You are about to edit a ShadowTiddler. Any changes will override the default system making future upgrades non-trivial. Are you sure you want to edit "$:/core/ui/ViewTemplate/subtitle"?
and It has NO content Type Set so perhaps you can delete that as well from you cardo version.
I also recommend pasting the default over the tiddler in case there is a subtle difference.
I imagine if you toggle cardio's plugin enable/disable you may or may not override your edit to the above tiddler.
FYI: I am not a cardio user, just trying to help
Tony