It was this one!

You are the Head Judge of a Modern PPTQ. Anthony controls Ajani, Mentor of Heroes. After combat he activates its second ability, looks at the top four cards of his library for some seconds. Finally he says “I’ll take the creature,” and puts one card into his hand without revealing and the rest on the bottom of his library.

Norman stops him and says, “Hey, you should have revealed me that card. Judge!”

When you get to the table, they tell you what happened, and Anthony shows you his hand with a Scavenging Ooze and a Windswept Heath, and tells you he picked the Ooze with Ajani’s ability.

What do you do?

Judges, feel free to discuss this scenario on Judge Apps!

Anthony has commited GPE-HCE. He has placed a card in his hand from a hidden set of cards without revealing to verify the legality of the action.

This paragraph of latest IPG should help us to find the fix for this scenario:

If the error involves one or more cards that were supposed to be revealed, the player reveals the set of cards that contains the unrevealed cards and his or her opponent chooses that many previously-unknown cards. Treat those as the unrevealed cards for any required actions. If the cards chosen would not legally be in the set as a result, they are treated as excess cards.

Since there is no information about previously known cards in the scenario, we will ask Norman to choose a card from Anthony’s hand and treat it like the one Anthony selected.
If Norman chooses the Ooze, there nothing else to do. But if he chooses the Fetchland, then we have to apply the next text to put that card in the appropriate zone.

Excess cards are returned to the correct zone. If that zone is the library, they should be shuffled into the random portion. The player does not repeat the instruction or partial instruction (if any) that caused the infraction.

The correct zone is the library, and even if that card would have been placed on the bottom of the library had Ajani’s ability been resolved correctly, IPG instructs us to shuffle it into the random portion of the library. That card wasn’t part of the set that went to the bottom (unless Anthony is cheating), so it’s simply treated as an excess card.