How to unlock an Open Ground Data Field

A created data field (number type) has suddenly become uneditable in openground professional - how do I change this?

The Data Field's name has changed to italics

I am using the Data Collector in conjunction with Professional, so when I perform data entry on the tablet I can edit the field but not afterwards in professional.

The field is used for calculations in other fields

The field is not mandatory

It is not a calculated field

I used to be able to edit the field after the fact and the calculated fields changed automatically - anyone know of a fix?