This is happening on my system as well. Markers do not appear on the timeline either. Latest 2020 version. If you hover at the top where the column should show next to Name etc., the Label Name popup appears, but it's blank all the way down.
I am having the same issue. I was seeing the labels column in my project window, yesterday. But due to system techincal issues that I was troublshooting, I uninstalled and reinstalled Premiere Pro and since that point the Label column,doesn't show up. I have label selected in my metadata options. I also tried unchecking it and then going back in and checking it, and still no Label in Project Window.
Quoting Neil: "It's an identified bug, it happens with projects from previous versions. The current suggested fix is to create a new project file, then go to the MediaBrowser panel, navigate to the original project file, and import that into the new project file.