Responsible Contact ID Field Value Disappears When Opening Case in a New Tab in Dynamics 365

What’s happening?

When opening a case in Dynamics 365 Customer Service in a different browser tab, the "responsiblecontactid" field value disappears from the form, even though the value is present on the server side. 

Reason:

The "Responsible Contact Id" field is a deprecated attribute. Due to recent platform enhancements in Dynamics 365, deprecated attributes no longer populate their values when a form is loaded in a new browser tab.

Resolution:

There are no plans to remove the ResponsibleContactId lookup attribute. Use the PrimaryContactId for new customizations or if you're migrating existing customizations that currently use ResponsibleContactId.

More information: Deprecations in Dynamics 365 Customer Service | Microsoft Learn