Extension cases created using save to case assigns the health post ID for owner_id. And, commcare report won't read or count from such cases unless the owner_id is blank ("-"). So, to solve this, I saved the value of owner_id as blank on save to case control as shown below. I also tried storing "-" on hidden value and saving it as owner_id.
And, it works as expected on commcarehq form player, however completing the form on a device/tablet throws an unknown error. Here is the screenshot.
I would appreciate any help.