A Very Festive Problem is a Lantern Rite Tale mission in Genshin Impact that will not become available until the second stage of the event. You will need to begin the quest on the event page, then go and speak with Herbalist Gui at the Bubu Pharmacy in Liyue.
Gui will ask you to deliver medicine to two different citizens down at the docks. Both will be marked on the map, so go and speak with them. Give them the medicine and then return to Gui.
Gui will not want a Xiao lantern for his business, but he will want one for himself and will ask you to make one for him.
To make a Xiao Lantern, you will need:
- 1 Lantern Fiber
- 1 Wick Material
- 1 Plaustrite Shard
You can get Lantern Fiber from any harvestable plant. If a plant exists in the game that you can collect, you will automatically get one Lantern Fiber when you pick it.
Wick Material will drop from Hilichurl-type enemies and Fatui Elites. You need to kill the enemy, as usual, and the material will drop from them. You can then pick it up like any other.
Plaustrite Shard can be obtained from any harvestable ore in the game, so any time you are smashing away at a rock, some will drop for you. You can also get it as a drop from Geovishap Hatchlings and Geovishaps. The final source is Stonehide Lawachurls. In this case, harvesting ore is definitely the easiest way to get it. You can then make the Lantern at any Alchemy bench.
After you give it to him, you need to wait until between 20:00 and 24:00 the following day. This is important, if you change the time to later that day, nothing will happen. You need to wait at least a full 24 hour period to progress the quest. You can do this in the main options menu by selecting the clock icon on the left of the screen.
Go and meet Gui on the nearby hill after the time has passed and he will release the lantern, ending the quest. You will receive 30 Primogems, 20000 Mora, and 100 Festive Fever.