Bug Type: Progression, Game Logic
These quests cannot be completed in the game at this time, despite being available to start. These are not due to bugs or glitches (such as happened to Sengoku characters with their Magnus prequests in the past), but due to unavailable NPCs or content normal players cannot access. (Note that these are all based on my experience on Reboot, I cannot speak to any quest that appear on other servers)
Dragon Rider, an Explorer quest. An old outdated mount quest that cannot be completed because the prerequisite quests, receiving a Hog and Silver Mane mount, are no longer accessible. This quest can be accepted from the 4th job instructors in Leafre, but cannot be progressed.
(Lv. 35) Amoria: The Sakura Garden, under the quest journal heading Victoria Island. This one is a bit weird now. Before, when old Amoria was still accessible, the problem with this quest was that the Sakura Cellions in Amoria didn't drop an essential quest item. Now Amoria is (normally) inaccessible altogether, and I'm honestly not sure this quest even appears in new character's Available quest lists. It's still listed in my old main character's available quest list, so I'm going ahead and listing it for now.
The Committee Challenges, Under Victoria Island. The first part of this quest, collecting Lazy Buffy marbles for Sabitrama in Sleepywood can be done, but the second part is undoable. Previously because it requires going to Omega Sector, which was closed until recently (though the second part of the quest could be started using a remote quest accepting item. It could not be turned in with a remote quest item though). Now that Omega Sector is back, the required NPC, Dr. Kim, does not react to this quest due to the revamps that have been done. I need to do this questline under other characters, as with the previous quest listed, I'm not sure if that one is even still available to newly made characters. Updates pending me having more free time.
The Missing Hero, under Leafre. This one is only impossible on Reboot due to the nature of the server. The last part of this quest requires a Nine Spirit's Egg from Horntail, but because that item acts like a Scroll, it does not drop on reboot, making the quest unable to be completed. After a recent patch, Nine Spirit's Egg suddenly starting dropping on Reboot, and I was personally able to finish this quest line. I haven't tested it on other characters, but as far as I'm aware, this one is now possible.
The Lantern at Mushroom Shrine, under Overseas Travel, related to Showa Town and Mushroom Shrine. This quest cannot be completed as previous changes to the Mushroom Shrine area have changed the monsters in the area. The quest requires killing Paper Lantern Ghost enemies and collecting the Worn Paper Lanterns they drop. The only place a monster of this type appears now is in the map Zipangu: Vanished Village. However, the Paper Lantern Ghosts there now do not count toward quest completion when killed, although the items they drop still do.
Eliminating Big Cloud Fox, same heading and areas as above. This quest requires killing 80 Big Cloud Foxes. As before, the current iteration of mushroom shrine does not have this monster anywhere that I can find.
Umi's Ambition, same heading and areas as above. This quest requires talking to the NPC Alien Gray in Omega Sector. Before, Omega Sector was closed and this NPC was inaccessible. Now, this NPC doesn't exist in the new Omega Sector.
Eliminating Ghosts, same heading and areas as above. This quest requires killing Nightghosts. There are no Nightghost monster available in-game at this time, in the Zipangu areas or out.
For a time I had the quest to kill Astaroth on Victoria Island active, which couldn't be completed because Astaroth's Demon Door no long exists. However, I forfeited that quest to build this list and now it's no longer listed under Available or receivable from the NPC, so I'm going to assume that one has already been patched out entirely? Otherwise that quest also belongs on this list.
This is all I could come up with at this time, having done nearly every quest currently available in-game over the last few months. I've only created about half of the available character types so I can't confirm that all of the unique character quests are functional, but so far there haven't been any other issues. If anyone else has found any outdated quests that can't be completed due to revamps and changes that cause broken quest logic (not straight up coding bugs like Princess No had for a while there), please add them to the list.