Cannot progress story with another Host despite being on the same story step

Hello,

I am no longer able to progress through the story with another player at the same step of the story and there is a permanent objective marker which I cannot remove on Seren (the NPC that increases item slots and capacity for food).

This issue started after beating Amaterasu for the first time and my story progress was at the step of rebuilding Minato where I needed to clear three tasks from Seren, Yataro and Tamakazura.

I completed Seren's task on my own and the progress for that step was completed (there was a checkmark next to the task).

After that, I joined a multiplayer lobby at the same point in the story which did not complete Seren's task at the time.

Upon joining this host, the game had informed me that I can still progress the story at the same time with this host.

We completed Seren's task on the host's world and then I returned to my world.

After checking the story progress, Seren's task was no longer completed and the objective marker was back on Seren despite me already clearing it on my save (and a 2nd time on the multiplayer lobby).

When I attempt to talk to Seren, she only provides me with regular dialogue and the objective marker remains.

After completing the other two tasks and I was able to progress to the next step of the story on my own.

However, now when I join another multiplayer lobby that should also be on the same story progress as my save, the game does not tell me that my save progress will be synced and when we progress through the story, I do not get the same progress on my save when I return to my world.

Would there be a way to fix my save to be able to progress with players at the same step of the story?

Also would there be a way to remove the permanent objective marker on Seren?

I have attached a screenshot of Seren with the permanent story objective icon alongside the current story objective on the top-left showing as a later part of the story as well as a screenshot of the map displaying the objective icon with a red circle pinging.