I found all the story parts and got access to all the archive videos, and it says "Unlocking all the Archives will unveil a Secret Twist in the final Epilogue".  I made sure they were all unlocked and then did another run through the dungeon and defeated the final boss.  There was no additional "Secret Twist". 

Hey,

when you're in the archive overview, next to the heading "Station Archives" it says 8/8 or 0/8?

If it says 0/8, it could be the bug or part of the bug.

If it says 8/8, then I have another bug. Because I have completed two archives in my game so far and also watched the respective videos, but I still have 0/8.

Yeah it says 0/8.  Protip: Just find the videos in the Endless Dungeon game files, the "secret twist" is called Outro2 or something.  To be honest I kinda figured it out on my own lol.  I used some details in the archive videos and in the levels to form my own head canon that is much more of a cool twist.

Hey,

Thanks for your reports. The progress toward unlocking all archives not updating is a Known Issue. You can find the entry in our public bug tracker here.