The TSV values are not available on object based portlets build on sub-objects like Assignment.
Steps to reproduce:
Navigate to Admin -> Studio -> Portlets
Create a grid portlet based on "Assignment" object (any sub-object can be used)
Navigate to List column section tab -> Fields
Create a New TSV field by using New button -> Time Scaled Value
Configure the field as below
Click on Save and return
Navigate to Layout section
Move the newly created TSV field to selected columns section along with few other fields
Save and Return
Now configure the Portlet on any Dashboard
Access the portlet and filter for any investment
The values under ETC TSV field are blank
Resolution
The time-scaled values (TSV) on the object based portlet work only with the first level master objects (eg. project). Assignment object being sub-object of project object the TSV for ETC field is not supported on the portlet build with assignment object. This is how the classic UI has been build to work.