Towards the end of the filling process the cylinder pressure rapidly and significantly drops. Does this mean my system is broken?
The rapid drop in the cylinder pressure shortly before the end of the charge does not constitute grounds for complaint, and instead, is normal and unavoidable from a technical standpoint.
Reason: The cylinder is filled approximately halfway with liquid carbon dioxide. You remove gaseous CO₂ from the cylinder; the corresponding share of the liquid CO₂ passes to the gaseous phase; the pressure remains constant. It isn’t until less CO₂ passes from the liquid phase to the gaseous phase that the cylinder pressure begins to drop.
This means your system is functioning normally.