You have applied a model rule for a list field. And it is not working and also not evaluating result for this field when creating a rule.
SAP Cloud for Customer
Reproducing the Issue
Go to Service work center.
Click on Tickets view.
Open any Ticket.
Navigate to any facet / header.
Try applying rule to a list field.
It is not working correctly or not evaluting result.
Rule editor and validation do not work for 1:n fields. Which means it only supports for fields which holds one value. For list or multi-value which is 1:n, this is not supported.
This is the behavior for tables inside the objects or for the Lists on the Views (Object Work List - OWL).
This is the expected system behavior.
Model Rule , validation rule, Rule Editor, 1:n fields, 1:1 fields, List fields, List field for Model rule , KBA , AP-RC-UIF-FLX , Page Layout & Key User Configuration , How To