Custom Non-Read-Only field values disappearing from form after SAVE in CRM 2015 On-Premise

I have a non-read-only field that a user enters a value into it.  After the user has saved the form, that field's value is now gone.

I have read what to do for read-only fields that are losing values.  What should I do in this case so that the field value is SAVED?

Thanks,

Michelle