1.Melt temperature. If too hot, resin may have degraded and degraded resin is difficult to eject.
2.Mold temperature. If too high, part may be sufficiently cool or rigid to eject properly.
3.Alignment of cores and cavities. If not properly aligned. Mold may be difficult to open and part will not eject easily.
4.Sprue. Check for damage to sprue , which could cause entire part to be ejected poorly. If sprue is too large ,material may be building up on the outside of the bushing.