rikaryo
Hi,
It seems to be issue when creating a new theme. I've shared with the team for further checking on this.
In the meantime, you can simply clone the header of the theme which you edited before saving as a new theme: /templates/ja_good/tpls/blocks/header/
For example, I assume that you edit theme 'Game', it will load the associated header file: /templates/ja_good/tpls/blocks/header/header_game.php
you then duplicate this file to have a new file: /templates/ja_good/tpls/blocks/header/header_red-ivt1.php
The error will be gone then.
Regards