Right, here's a solution from the german forums (translated by me, so sorry for any mistakes^^). When you're in the ruin of Jespars house, enter into console: "setstage mq11b80", "setstage mq11b85" (without the " obviously ;)). Now talk to Jespar (dialogue is fired in the first room of Jespars hideo...

Try lowering the HUD-opacity.

Alternatively, if that doesn't help, do you have anything activated in experimental multithreading? If so, deactivate and try again.
Activating One-Tweak might also help.

Schon mit setstage MQ12b 10 versucht? (bzw. einfach mal ein paar andere Zahlen dahinter eingegeben? Auf jeden Fall vorher speichern falls was schiefgeht.) Hier gibts noch einen Thread wo das Problem diskutiert wird/wurde und da war auch noch ein Quest stage aufgeführt, aber ich weiss leider nicht me...

Did you cremate Ryneus? Or activate him?

After he dies, you can activate him (press E^^), you get the choice to either cremate him or take the black pearl.

If you choose to cremate him the pearl gets added to your inventory too.

The pearl should be an amulet, so check there for the pearl.

You could try the launcher options to reduce the grass draw distance(?) *mine is at 0 to make finding bodies easier... not as pretty but still pretty enough :)* Also, experimental optimizations, don't know how that works, but if you have problems with blackscreens or strangely behaving quests, consi...

Glass Cannon Mage is basically someone with low defense and insane amount of damage.

Destroys everything very quick, but if that tactic doesn't work it's nearly instant death

The sticks is a bit hard if you wear heavy armor or have your weapons drawn. Go from the left one to the middle, then right one, then drop down and activate the other 2. I had some problems with that aswell, performance isn't my pc's strong suit^^ had to try it for about half an hour... Try sprintin...

Oh boy... let's see^^ I'm not too sure on that cause it's been a while but let's try^^ Travel to the Myrad(hope it's the right word, haven't played in english yet^^) tower. Follow the road north, I believe and somewhere should be a road to the east. Follow that, you go through some ruin where I don'...

It sometimes helps to revert to an earlier save where the message isn't there yet. Others have had the same problem with messages popping up (big thread in german forums). Here's something that 'could' help, can't say if it does (would definately try reloading first in case the workaround may break ...

First!!! Save your game and keep the save^^

Then, restart, the game, your pc, everything. If that doesn't work try some console magic

setStage MQ12b 5

should start the next quest if you speak with the Arch-whatever he is^^ (don't remember, Lexil or something?)