You mean to say that it grips the bar, but the pushrod does not retract and thus does not release the bar?
as far as I can recall (without the manuals beside me) the ex620 is your excessive alarm (EX, EXcessive), and it is likely alarming out because the pushrod cannot retract itself from the material, ie. it is going over its torque limit trying to retract from the remnant and throws up your alarm.
How hard is it to manually remove the remnant (I assume youve been just manually loading bars.. we all have to make parts even if its one bar at a time :P). Id check that first, and then once youve removed the remnant check the end of it. Check your pushrod collet, it may be too small. You say you're using tube, so perhaps it is crushing and forcing its way further into the pushrod collet as it is running?
Though I do have to admit it would seem logical that if it was too hard to remove that you would get an alarm as the pushrod grabs the bar during loading.
Start with your remnant, that should give you some indication of whats going on. If I have misread what exactly what is going on, could you explain a little better? Does the pushrod retract? or does the gripper just close, and then open and then bam alarm?
When in doubt, give someone a call at citizen, theyre great about helping out with problems, and theyre great people