Tried to help you with your problem. Maybe I didn't explain it well enough.
Where do you think the energy to extract, eject, reset hammer, strip new round from magazine, chamber it, lock rollers behind it, comes from? WIth underpowered ammo, any part of the operating cycle can become problematic. Your description sounds like there's not enough energy for the ejector lever to kick the empty case off the extractor and clear the ejection port.
I don't know why people get their brand new, military spec firearm, and then are surprised when they have function problems in the first 100 rounds of Billy Bob's Soft Shootin' bargain basement ammo.
Someone will come along and say "quality firearms should function with any kind of ammo" and "properly made firearms shouldn't need a break in." If so then HK's suck because nothing else would explain the number of posts from people who have exactly the same problem you describe in their brand new guns.
Good luck getting it worked out.
ETA: Try this stuff:
500 Rounds of Bulk 9mm Ammo by Winchester - 124gr FMJ It's even cheaper than the PMC when you buy 1000 rds. You want somethijng with the circle cross headstamp.