After migration from Foundation 12.1 to Evolve 20.2 the EmailAssignment could not be maintained with a promoted field in email subject line anymore. I've attached some hardcopies of the issue and what the settings which I've done maually in Evolve.
For this to work effectively '; please make sure there is no subject in the assignment message as it will overwrite the existing settings.
If this doesnt resolve the issue delete the promoted field and it’s rule. Create both again.