Thank you for the well written and useful answer. 

Unfortunately, this seems not to be the right fix for me because the date column is enabled in both the custom form styles window and the invoice itself. 

The thing that strikes me as odd is that the Email sent to my customer has the date column, but the attached PDF does not. (Which is the same when I preview the invoice)

Also worth noting is that when I preview the form template while customizing the form, I can see the date column. 

I have tried creating a new form, but the issue occurs in the new form as well.