Steps to reproduce

1. Go to /register page on storefront.
2. Fill in all fields.
3. Click on submit button.

Actual result:

Nothing happens on FT, no confirmation that user has been registered.

An error occurs 

MessageOriginCauseValue for required field definition 'customer_group' with language 'eng-GB' is empty  

Expected result:

User receives confirmation about registration.
USer is registered.