Unearth minions disappear if you out-range or out-run them. Which kills its functionality.

I was about to fight a boss, when again, noticed I had no Unearth minions. So I walked about 20 meters away to summon some and ran back to the boss. In the 2 seconds it took me to run to the boss from where I summoned them, every single one of them disappeared because I out-ranged them.