It’s Chaos.
Basically, a comparable issue like etali
When matching the activation gem, one of the following occurs :
I get a spell with full mana (yeah!)
I get a spell without mana
I get a spell added to the top of my library
Nothing.
//Edited Title - Tombstone
Scroll through for my post on this from a few weeks ago. There is one scenario you are missing.
If you have a full hand but your opponent does not, their next spell is fetched to their hand with full mana.
Cost me enough games that I stopped running the Wand (which sucks, because I really like it)
I can confirm that the team is aware of the issues where Chaos Wand fails to fetch a spell or places the spell into the opponents hand, but I will go ahead and relay the cases where you receive the spell with no Mana or where the spell is added to the top of your library for further investigation.
@Laeuftbeidir
In the instances when Chaos Wand fetched a Spell with no Mana, do you happen to recall what cards were fetched at the time?
Currently not, but since I run it in all my mono black decks I’ll make sure to take notes
Can confirm it’s still bugged. Wasn’t able to recreate fetching with no Mana, but fetching to my library is still a thing 
New thing? It fetches to my library when my hand is not full, but Gregs