A single hole located on the body, just below the shoulder/body junction.
But the FL resizing die has been hardened. Which means no small drill bit will cut a hole through it. The hardened steel die body is too hard for any drill bit to cut it.
I can't be certain that's the source of the problem. But from what you've described, it theoretically could be. Other die manufacturers do add the relief vent hole. And what you're experiencing may be the reason why.
Not sure wbat the hardness of the dies are but a carbide hardened die drill bit shoukd work. This is not the same as a twisted carbide(typical drill bit).
Heres a link to an example of what I am speaking of. (not a specific recommedation for a brand just an example)
http://www.newmantools.com/drills/drctdie.htm
Make sure to keep it flooded with coolant. Any machine shop should be able to do it if it will work. Its what I used to drill gas ports thru nitrided barrels.