The best solution is to ignore the recap - it is broken.
You have to start the questline in Dalaran as some have said.
This allowed me to enter Dornugal, fly and set HS.
It also allowed me to start unlocking World Quests, Delves and Weekly quests
Good luck
The following is the workaround I have found.
Once you get to the stuck part, exit recap. Then hit Shift-J , select suggest content tab and click the lower right box to Accept Quest for The War Within and accept the quest. Click the teleport to silithus scroll and talk to Jaina and complete the quest. Then talk to Thrall (you may want to turn on low level quests depending on your level. When talking to Thrall tell him you have heard the tale before. You should then be in front of Brann Bronzebard after loading. Go to your map and back out to the Isle of Dorn Map and on the western part of the map you should see a campaign quest. (or take the quest from Brann and then click the table behind you and select Isle of Dorn if you want it to give you a quest to go se Jaina) Go follow that chain until you gain your skyriding.
Next you just have to get to 80 (follow the quest chain or any other method you want).
Once you hit 80, you have the option to talk to Brann to be able to skip content. Do this, once done, you can then go back into recap and speak to Merrix to complete the quest and complete this recap, and then go into the late game recap if desired.
This fixed both of my broken characters.
Also having this issue!
I was able to resolve this issue by 1) Going to silthius and starting the full questline. 2) Play all the way through the main Isle of Dorn quest. 3) After the meadery when âthe first blowâ completes.4) go back to the recap. - I was able to go back to the recap and talk to merrix to complete it. this giving me full credit for the campaign.
This is completely unacceptable.
This doesnt work after some point because the Adventure Guide will switch over to 11.2.7 story (the new quests) and refuses to give you TWW. No way to start TWW. Completing the Dragonflight âThe Harbingerâ quests doesnât start TWW. Itâs totally screwed.
Iâm also stuck here. Came back from Dragonflight. Havenât done any TWW until the Catchup.
Same issue here.
You shouldnât have to do that tho.
4 days, no blue post on any thread about this issue.
Not only that, but they didnât even disable the quest in-game, so people who are unaware of the bug are still getting trapped by it. At least with the Remix transfer bug they patched out the button so no-one could encounter it
Probably wonât get anything until Monday at the earliest and even then I doubt it.
5 days of a bug that breaks a new feature for returning players without even an acknowledgement from Blizzard. Support does nothing but refer you to irrelevant third-party sites. Completely unacceptable
Went to Silithus and progressed the regular campaign through turning in Recompense (Convergence is enough to make Merrix show up, but not to allow the turn-in) as some have suggested, and I can move on now. Turned in Recompense, went back to Valdrakken, used the book, asked it what it could show me, selected TWW, backed out, reopened it, allowing me to tell it I was lost, then returned to Dornogal and Merrix had the dialogue option to proceed though he didnât have the ? over his head.
This should not at all be necessary, but it was faster than waiting on a fix. And you unlock flight in Dorn early in this process, as should have happened our first time on the beach. This is a critical progression-stopping bug with the quest flags, and it doesnât even seem to be acknowledged yet.
For anyone who does the workaround, be aware that when youâre in Dalaran, you need to pick up all of the quests in the middle chamber, even though some of them are not labeled as campaign quests, they will prevent picking up the next campaign quest if not completed. Once youâre actually in TWW content, itâs a straightforward path through the first zone of the campaign.
This really should have been fixed by now without requiring new players to figure out where to go to perform workarounds in a game theyâre not yet familiar with.
I can verify that completing the TWW campaign through The First Blow achievement is a workaround. If youâre 80 it is infuriatingly easy to miss some quests because they will all be low level. After you finish Recompense, you can simply port back into the Recap quest through the Tome of History and Merrix will be where he is supposed to be. What a pointless waste of time.
Also having this issue! Level 76, no Merrix for turn-in. Decided to switch to an alt and will attempt it with that toon next.
Having this issue also, encountered it 2 days ago. Tried one of the first work around suggested, got stuck, did the unstuck support, waited HOURS, finally logged in, completed the first achievement for Isle Of Dorn as suggested above, went back into recap, and I am stuck AGAIN. This is so annoying. I have now done the unstuck support for a second time and hopefully once I am unstuck, it will be fixed. I have been able to fly in most of the zone except one small part of the city, lol. I also donât have a button for peruse tome when I am lost? It says I should be able to but thereâs no option. How has this been an issue for days yet thereâs not even a response yet??? I do see thereâs maintenance Tuesday, hopefully theyâll fix itâŚ. Ugh. 
It worked! What I did was open the adventure guide Shift J, click the suggested content tab and selected the war within quest line. Played the questline all the way through the meadery until you get The First Blow achievement storyline. Then I went back to Valdrakken and used the Tome of History there because the one in Dornogal is bugged, went back to recap mode, turned in the Return to Dornogal quest and Merrix was there and was finally able to complete it.
The quest Shadowy Pursuits recap is still bugged though, the Tome only has a teleport option and it takes me to Anduins and Faerins location outside the Skittering Beach delve with no way to advance.
Running into the same issue. Canât fathom how they havenât identified this yet
Bump, just finished got to this part in a group and we both ran into this Merrix issue. We just returned from a 10yr hiatus and was hoping this would be a good way to catch up⌠starting to regret the purchase not even 10hrs in.