@two-jay
****NEW FIX TO TRY****
So it seems to be a common occurrence for people to get stuck on this mission and I have been trying for three hours to get this cutscene to activate.
Fixes I have tried that may work for you...
-Changing settings to ultra (If your PC can't handle ultra, you should be able to switch it to the highest settings that you can)
-Changing everything to the lowest possible setting and putting V-sync as "adaptive".
-Not hitting any buttons when talking to the two prisoners and watching the full cutscene.
So far, none of these have worked and all of the posts tell us to wait for an ubisoft fix if non of these work.
In my case, I use an Xbox one controller on PC to play AC Valhalla and as soon as I unplugged my controller with my settings on Ultra, the cutscene activated
I know getting stuck here is extremely frustrating so hopefully this works for others as well.