Please post here if this has ever happened to you.
There are numerous ways to bug the quest advance mechanic in this chain.
Here are some ways I would like to post to help others avoid disappointment.
If you are doing Threnal for the first time, do not repeat east or west. Instead, ask if there is any more to do.
After you have done east and west, go back to first quest giver to ask again if there is any more to do.
Report to south and complete.
After getting chain end reward, do not simply repeat east or west thinking this will allow you to go to south again.
Before repeating any of the three, you need to reset all three or you will not be on the chain for south.
Hope this helps save you some time and frustration.
This has been a known issue for the past 5 years, but has not been resolved. The same type of problem with VON was addressed, but this was left in the PRE-FIX state.
In addition, the bug report link from my ddo is down again.