Glocks always shoot left of center for me, fortunately there are choices...
That is true for many individuals due to hand fit and trigger issues. I am one of those who has to shoot a Glock like a Glock and not everything else to preclude this, but once those issues are addressed, there are some Individual Glocks which shoot left / high left.
This has been noted in batches of LE guns being fired by skilled shooters / instructors.
Another weird thing is I've seen some Glocks particularly Gen 4 G17's which shoot high left with certain ammo and dead on with other Ammo. I was just discussing this with an instructor from another agency re: his agency's new SWAT guns. They have some guns where their duty load shoot POA/POI but their practice load consistently hits high left with certain individual guns.
I've seen front sights "clocked" before, usually along an 11 o'clock / 5 o'clock axis - usually happens when tightening down the front if the tenon does not completely fill the hole. It is certainly a cause, but not the sole cause of guns shooting left.
I've never seen a Glock slide with the front sight hole off center but I suppose it's possible. I'd be curious to see if anyone else has seen that.