Jiquani's Machinarium unaccessible after quest completed

Once you find all soul cores and open/complete Jiquani's map & go further, the doors are still locked & there's no more soul cores in map to reopen the doors.

I missed Blackjaw's kill so i was trying to go back but its inaccessible, even if trying to go from other entrance coming from Jiquani's Sanctum waypoints, its still locked.