Greetings Donau,
Just a quick question to clarify, have you tried clicking on all of the Vendrien Guard prisoners when Fifth Eye comes over to the prisoner's posts? I have personally made the mistake before of clicking on the wrong NPC, and repeatedly getting the same barks and thought I had hit a blocker.
Hopefully that will help solve your problem, but if it does not help you get past this point you can send us a copy of your output log and a save file if you would be so kind.
You can find your output log here: \SteamLibrary\steamapps\common\Tyranny\Tyranny_Data\output_log.txt
and your save file should be here: C:\Users\[[USER NAME]]\Saved Games\Tyranny
Please let me know if you have any further questions, and thank you so much for your time and consideration in the matter. Hail Kyros!
-Best,
Ian