This is because of the game’s anti-cheat checksum. The game checks Homecities for the proper checksum to verify that your HC was built legitimately ingame and not made in a text editor (since with a text editor you can have more than 25 cards). If there’s anything in the Homecity xml that’s different from what the checksum says it should be, then the HC is considered invalid.
Your only option is to delete all your decks and then rename your Homecity and explorer to what names you want to show up in your scenario, then build your scenario deck, and copy over the HC file without making any external changes to it, only then it will load.