Zombiefied piglins tries to pick up all nearby golden swords. When a zombiefied piglin picks up a bunch of swords it drops them and pick them up again. This causes major lag and as the zombiefied piglin keep picking up the sword, the swords won't despawn.
I've experienced this bug in my goldfarm. With a looting III sword the Zombiefied piglins I kill drop a lot more sword than they usually would. And my pick up system is to slow to pick up all the items they drop hence the reason a lot of gold swords becomes available to them to pick up.