Hey!
The only necessary check to get the scene with Voss is to have met and spoken with Vlaakith at the Creche. I have passed on your report and the steps to the team so they can look into what might have caused the scene not to trigger.
If you still want to turn Lae'zel against Vlaakith you can do the following during a certain camp visit in Act 3 (tagging as spoilers just in case):
When Vlaakith visits you in camp at the start of Act 3, you can succeed a difficult roll and switch her to siding with Orpheus, even without Voss, which would allow the romance to continue. It sounds like you might be past this event already, but in case you still have not had this camp event.
