I used to be able to filter a subset of files within a folder in and each thumbnail would have a number at the top left corner showing me the sequence number (e.g. the 5th file in the sequence would have the number 5 in the top left corner of the thumbnail image. Now that information is missing. How do I enable that feature?
That is a View Setting and only available with the Compact Cell View.
Ctrl + j keys or View menu item the View Options. In the Show Grid extras select Compact Cells.
A known issue.
See the official reply to a post at- Lightroom CC 2015.7: Badge numbers in Grid view not visible on Sierra | Photoshop Family Customer Community
Until an update corrects then only the "small" sequence number are available.