You have a process that sends an Action Item to the Resource Manager when a timsheet is submitted. You are able to see the Action Items in the Modern UX, however when you click on the link it redirects to Custom Objects, and an “Invalid Custom Object” error is received.
Release : 16.0.1
DE68523
This was reviewed by engineering and currently, a link to Timesheets from Action Items in the Modern UX is not available.
In 16.1.1, this link is removed to avoid confusion.