This is a known bug and has been fixed in 21.1. New registers need to be added via the database.
Please raise a new case for each register change and include the following information:
DESCRIPTION: Any chosen name.
HAS_CATEGORIES_FLAG: 'Y' / 'N' depending on whether the register will have categories.
CONTEXT_FLAG: 'A' / 'C' / 'B' for Adults / Children / Both contexts.
START_DATE: getdate() can be used to make that from 'now'.
END_DATE: NULL should be the likely choice.
IS_CHILD_PROTECTION_FLAG: 'N' (unless adding a Child Protection Register in which case 'Y' but this should not be required as the Child Protection register is contained in the Customer Led Configuration build).