Are you certain the rest of your filters/settings for this calendar grouping with that custom label would be pulling in results? If yes, are you checking they're pulling the correct field? When adding a custom label, you'd start typing the field name but then select it from the options that show in the label area. You'll also need to separate them by { } Here is an example of how a custom field after saved would show - this is task name then project name.

Also check you're setting this up in an appropriate tab to filter in objects by either tasks, projects or issues:

If this helped you, please mark correct to help others : )