Forbidden Reach skip didn't unlock Zskera Vaults

Before access to the Vault can be gained, the Dragonscale Expedition first needs to set up in the area, which means starting with the quest Helping Hand and Claw.

You can find the full requirements on the appropriate WoWhead Guide: Zskera Vaults

The only quests it will NOT let you skip are the Zskera Vault quests, which include the 6 Keys. Questline here.