1) The sword plans come from the treasure chests in both the Fogstone Depths and the Fogstone Cavern (so it was a disappointment that we didn't get something new from the second chest).
2&3) No. It's a known issue for every player, so the Devs tweaked Trouble Afoot so that it's harder to "complete" (because we don't want to complete it until they fix this), and then they disabled the follow-up quest, which I think is Clearing the Fog. They were not able to figure out how to get the Lagoon Entrance to just become permanent yet, as the original developer is no longer on the team and didn't leave notes.
4) All questions that we hope to get answers for once the next Chapter is released. For context, the Lagoon and Fogstone Mines are new areas that were only opened up early 2022.