I have the past 3 Enchanters Writs uncompleted and had to abandon them. Opened a Bug reports for all 3. None have finished.
Always on the Discover X stone. It will not recognize the previously discovered stones.
By "discover" I'm assuming you mean obtain/harvest?
It would be helpful to know exactly which requested rune is bugged. Normally, if you have the requested rune in your inventory the quest should update. If you have one in your bank, it should update once you remove it from the bank to your inventory. Or, if you harvest it from a node, it should update.
Is it a potency or essence or aspect rune? Are none of the three types of Enchanting writs working for you? Any additional info, with screen shots, would help in identifying the problem.
If it is not seeing the stone in your inventory (which has not happened to me in forever since they fixed this) just drop the stone in the bank, then take it back out again.
Enjoy the game, life is what you really want to be worried about.
PakKat "Everything was going well, until I died"
Gary Gravestink "I am glad you died, I needed the help"