We had something similar. We used improved invisibility to start that quest and worked for us.
But yeah, even now a month later and several patches, and talking with Larian support, this quest is still bugged. We might have to skip it, which sucks, since my co op partner romanced Wyll. First time I've felt slightly aggrevated when it comes to this game. Would have loved to have seen the new cutscene, progressed the romance, but.. no. Just minecraft blocks and a super bugged Wyrmway quest, from start to finish.
Here's hoping no one else get this problem.
