RE: Fields on Form not locking / unlocking.
Hi,
By lock, did you mean making the field read only?
If yes, please check Field is Read-only property in field properties, as shown below:

The lock property you mentioned is to make sure field is not removed from the form (this is to avoid dependency issues). For instance, if you refer a field in Java Script and it is not available on the form, it will throw exception. Hence, we lock the field so we do not remove it accidentally.
Hope this solves your problem.
Best,
Wahaj
(if it helps, mark it verified)