Steps to recreate:

1. Continue Magnus till "Girl who lost the sea" quest 

2. Get into the instance

No quest shows up at all, either the girl or the bonfire, no quest to accept

Tried forefiting the quest, escaping Abyss, restart the game, restart PC, nothing works, seems other players are experiencing the same issue as well on Reddit, Can't progress throught Magnus questline anymore, game breaking, questline is now stuck. Seems to be a new bug after the update.

Hi, since it seemed to be the solution to another issue regarding the main quest , please check that you have all quest types active. For some reason, some main quests are filtered out if you dont have all types active.

Still not working. Please fix ASAP.

when will this be fixed cause im stuck here aswell and there isnt a solution about how to fix it

Please check that you have all Quest types activated in the O menu. There currently is a known issue where entering the Magnus disables most quest types, which will leave you unable to accept quests for the storyline.

That is not the issue. It MUST be bugged because I have having the same issue and yes the quest is activated. 

Can you post a screenshot of your questwindow to confirm all questtypes are enabled and look like this:

I don't think you are lying, but in most cases the players misunderstood that this is the problem.