Hey there @goattron, @G0dL1k3D3v1l, @Ashlynnw904 and @fpalomo1 - I sincerely apologise that your updates to this thread were not replied to sooner.
I am hoping that you all will have recovered access to the "Way of the Berserker" preorder bonus / Ubisoft Connect reward by now, but should any of you still be encountering difficulties, can you please update us as to which platform(s) you are playing Assassin's Creed Valhalla on, how you acquired the quest, and if you can find the initial letter in the mailbox in Eivor's room? Can you also please tell me whether you have reinstalled the game as part of your troubleshooting?
If you had started the questline but it vanished, can you remember on which objective it disappeared?
Thank you in advance for any additional information provided!