Essence of Umbra quest

Report code 32,094,389

In Act6, Shavronne bossfight ended with Sin landing and not doing anything further.
It was possible to descend into Warden's chamber, but there was no exit to prisoner's gate, and quest Essence of Umbra wasn't completed. Prisoners gate beacon on the world map was unlocked, but it was unusable due to missing quest conditions.

Bug didn't persist on second time when I opened another instance, but I thought I should report it anyway.
In case it might be helpful there are only two differences between instances – I opened incursion on bugged run but didn't talk to Alva on second run, also Shavronne herself didn't do any special voiced attacks on the bugged run ("Let me beautify you" etc), only summoned stationary books and then promptly skipped to the last phase.

Hardly descriptive screenshot with bugged quest below.
Sin's dialog contains only goodbye, but on the second try when the quest actually completed, Sin would always tell the same lines every time you click on him, not letting you have any dialog window. I don't remember if this is a proper behavior or not.