I am trying to edit the navigation bar for the Ringcentral Lightning app. I receive this error:

An error occurred while trying to update the record. Please try again.

Cannot modify managed object: entity=TabSet, component=02u50000000bIi6, field=UtilityBarId, state=installed: newValue='null', oldValue='0M050000000L06X'

Screenshot: https://www.screencast.com/t/OaeYEtLWL

Any ideas?