Unable to see the Process Instances list in the process model view

A Score Level 1

Appian System Administrators are unable to see the Process Instances list in the process model view. This is happening for all process models in staging and prod environment.

Steps: 
Open any process model.
Click "Process Instances" Icon.
Apply "All Process Instances" filter to Status dropdown.
No instances are listed.

For the same process models, able to view the instances in Designer monitoring tab. Could someone advise on this issue.

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