I had the same problem: nothing happens after talking to Gabe. However, the Balmorra bonus series is part of today's conquest objectives, and if you grant mission from that it gives you a mission to talk to Gabe. After doing that, the conversation with Gabe ends with the bonus series starting like it should.

Stuck on loading screen. Non-steam version Edit: worked fine on the second try, so maybe it was a one-time thing