What is happening:
At the stage in the quest where the player is told to enter the mines to talk to Geode, both Geode and Stun Law are missing from the Mine entrance chamber. No quest marker is visible in the room, and the only NPC visible is Silver Shimmer.
In fact, my other characters show a "?" icon over Geode's head, but they do not have the Artisan Talent Mark quest in their logs.
What should be happening:
Geode and Stun Law should be visible, with Geode able to converse with the player to continue the Artisan Talent Mark quest. Other characters should not have the quest marker showing above Geode's head.
Steps to reproduce the issue:
Create a new pony (in this case, a unicorn).
Start "Only Shooting Stars Break The Mold"
Follow the quest instructions until told to enter the mines.
If Geode is absent, look at the mine entrance with a different character.
Screenshots with descriptions here.