The O2 cylinders in question are definitely those of the pax system.
From the 744 systems manual:
"The passenger oxygen system is a continuous-flow system that automatically provides oxygen for passengers whenever the cabin pressure altitude reaches a nominal 13,875 feet or higher. During the first few seconds, the control unit produces a pressure surge that releases the oxygen mask stowage doors and permits the masks to drop within reach of the passengers"
Given that the pax O2 system had been 'compromised'.. it's probable that insufficient pressure was available to all mask stowage doors, preventing some from opening.
Similarly, insufficient O2 pressure in the distribution system may have resulted in a reduced amount/loss of O2 available at some locations.
This is my opinion only (as a pilot, not as a LAME).