I am not sure I am on the right changeset here, but there were several problematic changes to the coastline in northern Russia around this area. The coastline moved quite a lot, you can see that here  https://osmdata.openstreetmap.de/internal/coastline/ . I am not familiar with that area but just looking at it it seems that that large river delta is at least partially tidal and should therefore be classified as ocean water, not inland water as it was before. For the time being coastline processing is halted until this issue is resolved.