So i have had this happen to me a few times, i go mine a cobalt ore node. I get my mining level. It gives me 0 ore and says that that item is already in use.
The node would stay there as if it wasnt mined but becomes untargetable for mining. As a hunter i did track humanoid and beasts but noone was there.
It’s a phasing bug I’ve noticed if I enter a different phase as I get close to the mine it bugs out. You’ll see big letters above your char telling you your in a different part of the zone and it bugs the node cause phasing.
I’ve had 100’s of bugged nodes. You actually get the skill from mining it then you get no Ore and it says “This mob contains no Loot”
Oddly the same nodes that are bugged in Retail in WG are bugged in Classic. However there seems to be even more around the map and some other internal problem.