Did you create a Deity Category header and assign it a Deity Category Order Group number not in use - and do the same for your deity?
Basically there's a process for each pantheon you create where you can copy a "header" record and put a sort order in.
I'll paraphrase it rather than make you go searching:
1. Get in editor.
2. Find the Deity tab in the General section.
3. Choose to New (Copy) a deity.
- Find one that starts with {bmp npcclass} - this is a header record
- You will see that your copy has the Show Only box checked and has a Deity Category and Deity Category Order Group
- Change your Deity Category to one you want or create a new one.
- If you are creating a new one make sure to change the Deity Category Order Group as well
Now when you want to add actual selectable deities to fall under this header you need to make sure both the Deity Category and Deity Category Order Group match the header's values (So if you made a custom Eberron Pantheon with Order Group number 30, all of your Eberron gods need to have this category and group number to match with).