Today I got around to finishing Sybille's "Kill the Vampires" quest. When I returned to Solitude to collect my reward, however, I found a problem: Sybille had vanished. I was able mark the current quest goal (telling Sybille the vampire is dead), but no quest marker appeared on my map. She would never appear in her customary place in the Solitude throne room.

Using the moveto console command, I did finally find her, sleeping in a nearby bed.

Apparently she now spends 24 hours of every day sleeping. I get the impression she's supposed to start sleeping during the day, but instead she's just always sleeping.

By carefully digging back through hundreds of saves, I managed to pinpoint exactly when she "disappeared". Apparently, completing "The Wolf Queen" puts Sybille to sleep for the rest of eternity. I've tested this with consistent results: while on the Wolf Queen quest, I can check in on her and say hi. As soon as I finish the quest, (by handing Potema's remains to Styrr,) Sybille teleports into bed.

It's worth noting that Sybille had already given me the Vampire quest when I got the Potema quest, so it's possible the two quests glitched each other in some way.

Since I did finally find her, it doesn't look like there's any permanent damage done (unlike that one quest in Markarth...) but still, it's pretty weird. Anyone know if there's any way to fix this?

That is weird, but she's pretty much room decoration after that quest anyway, so no loss.

Maybe you could try some console commands? IDK of any, but there must be something that if used on her can reset her.. schedule?

Ran into this as well. You can wake her if you need her shop, so not a big deal.