Has happened twice to me on solo flawlesses, once yesterday when there were no server issues, and once a few hours ago concurrent with server issues (if that matters). I've attached videos of me going through the traversal sections before the encounter just in case. Relevant moments are 4:45 and 12:10, and then I backtrack as far as possible and come back, but the issue doesn't resolve. I've made it there without this issue happening too, so it's not fully consistent.