Apparently there was a fairly serious bug with Alchemy and discovering potions/flasks/transmutes last night, so Blizzard has hot fixed it to no longer be possible to make a discovery for now.
We have been working on the resolution of a serious exploit in game which has led to certain consequences that we wanted everyone to be aware of. A hot fix has been recently applied to the alchemy profession, with regards to discoveries. For the time being, we have disabled all chance of a discovery, until we can implement the proper fix through a patch , as we can not resolve this matter solely with hot fixes. We apologize for the necessary but temporary removal of discoveries, and are working to have them re-implemented with an upcoming content patch.