After you kill Durnehviir, there will be a prompt to search him but it is impossible to do so.
Sometimes after you retrieve your fragmented soul, the stairs
leading back to Volkihar Castle on the return trip will be unusable and
be part pixelated and you will walk right through them. Re-load a
previous save to correct.
If you try to ride through the portal on the horse, Arvak, it will
make you dismount. After you dismount it can cause your screen to turn
black. Nothing happens after that, besides music and seeing a black
screen. The way to get out of it is to turn off your game, seeing as you
cannot access the start menu.
Immediately upon leaving the Boneyard, it is possible to attack
Durnehviir before he begins dialogue with you. This may make him hostile
or at least prevent dialogue from occuring, making it impossible to
obtain the "Summon Durnehviir" shout and by extension the "Soul Tear"
shout.
Valerica will sometimes not move when returning to her after killing the Boneyard Keepers.

Enter the Boneyard and defeat Durnehviir, press the "~" key to open console, and type tcl
then press enter. You should be able to fly and move through objects;
go to the Elder Scroll case and enter the container to pick up the
scroll. This will trigger the next stage of the quest, and solve the bug
without creating the later bug in the quest Unseen Visions.
哭了……