Mag or mag block issue?

[Caduceus]

Hi all
Just installed a Hahn block on an SBR and topped it with a PSA 7.5" upper. Using 2 different ASC mags, 115 and 124gr ball worked fine, but 147 HST wouldn't feed. The bolt hold open was also inconsistent.

Using a PSA glock lower, the upper fed all the above, including the 147s.

I've read good things about Hahn blocks, so I'm wondering if this is most likely a magazine, block or ammo?

Any thoughts?