I have a site I manage that uses a "Multi-Select" HTML field type. I do not use the field so I cannot say exactly how recently but no more than the last month our field stopped being able to be edited or shown in search forms.
If I switch to checkboxes it works perfectly. If I switch back Multi-Select I get the same problem and when I save I get the error, "Please enter valid - Data and Input Field Type."
It is like it is trying to use the pre-CiviCRM 4.5 form element. I do not know how that could be.
I am running CiviCRM 5.28.2 in Drupal 7.
Any help is greatly appreciated.