With the "Prevent change mail" option enabled, the "email" field in the profile becomes disabled. This results in that field not being passed through with the rest of the form on saving the profile, then WordPress complains that no email has been set (which is required).
With the "Prevent change mail" option enabled, the "email" field in the profile becomes
disabled. This results in that field not being passed through with the rest of the form on saving the profile, then WordPress complains that no email has been set (which is required).The field should instead be set to
readonly(https://www.w3schools.com/TAGs/att_input_readonly.asp), which will also grey out the field but still pass it through the form.