When a record has a null two option field, and the current user is being limited to only reading the field via a field security profile, auto save will not invoke nor can a manual save be done when the field is formatted as a checkbox

Repro Steps:
Create a new entity

Create a new record for this entity

Create a new Two Option field, also enable field security (on the created record - the boolean field is now null)

Add the new field to the form, format the field as a checkbox

Create a field security profile, make sure on this field you assign only Read access

On a non system admin user, make sure their security role has full permissions to new entity and add the user to the field security that can only read the new bool field

Open the existing record as the limited user, when trying to make a change to other form data, you will not be able to save.
Formatting the field to radio buttons solves the problem