Factorio Forums

As you can see, the stack inserter (also tried with fast inserter) get stucked after few successful inserts. Long handed inserter is not affected with this issue.

If the right side is close to full speed it can not grab from this position. Post the save please.

I've edited the first post and attached the save file.

This is similar to the burner-inserter can't pick up from fast belts scenario: the available space for an inserter to pick up from an underground belt is tiny and at full speed the inserter can't grab items off the express underground belt.