Using Windows 7 if that is relevant:
tl;dr: In multiplayer sometimes pressure plates glitch due to multiple players walking over them at the same time thus causing some riddles to become insolvable. Look at the bottom of the post for a possible solution of this problem.
My Story:
So I guess the developers are pretty much aware of that issue by now but as I struggled with this for the second time now I might as well just write down what I've experienced just now.
So I'm currently on a lan-party with some friends playing hammerwatch, having a good time... Until we reached floor 11 where we just ran across a riddle trying to brute-force solving it. Worked on another riddle as well so why not here... except it didn't and the riddle broke.
This was actually the second time I experienced this but this time I wanted to get the 100% ending in the campaign so this was unacceptable... So I turned to memory hacking to see if I could fix the problem. (Note that I never did anything like that before so most of the time I was just figuring out how to get the results I wanted)
At first I figured I had to find the switches. I thougt that maybe one of the switches glitched to 0 or 1 if it should be the other way around, thus making the riddle insolvable.
After a bit trial and error and watching values changing, searching for unchanging etc. I found them, turning from 0 to 256 (1 byte I guess).
Then I tried to map them to the numpad values 1-9 (as they are in this neat 3x3 grid). But then I saw that each field would change 2 values...
So one for the actual value and one for the sprite, alright. Mapped those out and got 18 memory adresses... So there should be a value that didn't fit... but there was none such value, everything was fine. So I again, searched for values which changed if I would go along those pressure plates. Solved the riddle, looked for changed values, unsolved it, looked again... And then I saw a strange number "24" in the unsolved state. After solving the riddle the number became "15". Activating just one button and it was "16". So obviously the pressure plates where decreasing a value, but the value was too damn high to ever reach 0. So I just set it to zero and activated/deactivated a button so it went from 0 -> 1 -> 0... and the riddle was solved.
So I guess the pressure plates decrease from a value of "9" and the portal activates as soon as the values reaches 0 BUT the value also increments when deactivating a glowing shiny piece. So the glitch probably caused the variable to increment too much, making the riddle impossible to solve.
This problem could be solved if you gave every button a bool value or something along those lines and every pressure plate looks up if all the bool values are set. This is a bit more costly and a bit brainfuck to implement I guess, but it should not be able to glitch like it does at the moment.Here is the entire story in one picture, the line that is selected in the top frame is the one I had to set the memory to 0 in order for the riddle to work.
Thanks for your time and reading my story. I will now go with my friends and beat that dragons ass.
