The quest marker are not working properly from the part 7 (included) to the end.

Hmmm... there is location info on every starter and finisher. There is location info for Athrikus Narassin and Athrikus Narassin's Head (step 8). Step 7 is just simply run here and turn in quest to get next step... unless.

What level are you?
You have to be a min level of 20 to do step 6 and a min level of 23 to do step 7.

Level 27 for part 8 and level 28 for the final quest in the chain.

I was 31 at this moment
This quest is really long and I will understand if this fix is not a priority.
Anyway I solved this quest very easily without the markers.

I think I may see the issue. In Step 7 the quest title changes to "The Tower of Althalaxx part 7" then The Tower of Althalaxx part 8". Step 9 has the original title but without properly recording the previous two steps as complete, it won't show you markers for step 9.

Yep. Quest titles were wrong. Fixed and checked in.