During the dungeon break flashback (ch 19), a worker had a device(?) Showing that the dungeon was 100% cleared but when yiseon began resoring the area the device showed 99% cleared
What if he was the reason the portal (?) Reopened. Maybe he accidentally "restored" it too. Since he's the only s class restorer it might be a hidden power or something.
That would actually make him the reason his friends died and I don't think I could handle that.
(Recently binged this, idk if someone already made this connection)
(Also, most of the plot went straight over my head so this might just be nonsense)