Found a Fix on youtube. Thank you for your time however.

The npc for the fishing mystery appeared finally. Visited Lunden once again to take video footage. I used the time aswell to reload and meditate as i did already in the past. Eventuelly the npc appeared and i was able to speak with her.
The second mystery however is still not working for me:

After i finished the questline in Lunden, i was not able to finish either riddles at the river. The first one where you have to dive/fish for the sunken goods can not be finished, because the npc's for it are gone/missing. The second is not working because i moved the vases with soup and movable walls before the npc to be freed even spawned. Therefore the movable walls were stuck into the vases or standing on top of them later. So you were not able to either carry the vases away nor move the movable walls.