have faced this issue that when the particular ui field/ cell is Read Only then even though if there is a validation error that is associated with that field is not shown means it will not highlight or show red triangular symbol on that field , so it will be difficult for user to locate that property.

By marking below check box in Presentation tab will make the error visible by red triangular symbol visible in case of any validation error

"show validation message in read only mode"  (Read only format) needs to be checked.