Symptoms

setVisible() and setDisplay() are working as expected but when these APIs used with setMandatory(), setVisible/setDisplay is not honored. 

Release

Istanbul, Jakarta, Kingston, London 

Cause

From Istanbul onwards, we specifically and intentionally block setVisible or setDisplay calls on Mandatory fields to prevent scenarios where a field is mandatory, but not visible to be populated. This is designed functionality that is behaving as expected.

Resolution

In order to display and make fields mandatory at the same time:

-- Use UI Policies instead of client script. Its also recommended using UI Policies over client script due some of the benefits check this doc: Use UI policy instead of a client script

-- If UI Policy is not helping you to achieve your functionality use setMandatory and setVisible in two separate client scripts.