finally I got it to work on the pressure plates puzzle after going out and in again about four or five times
That matches the experience of some of the players who posted at the
Steam forum.
They have to redo the puzzle several times, exiting the area to reset the puzzle each time, and after multiple repeats the puzzle finally decides to work.
Why this happens is a mystery.
Glad you finally got through.
I'm not even sure that it IS a GOG bug
The problem is not unique to the GOG version and has nothing to do with GOG.
It's a problem with the game.
If the developer didn't fix the problem in the latest patch, maybe it was because he couldn't reproduce the bug on his computer.
You may have to use a saved game.
Chrissie has offered to use your save to play past this spot.
That's probably the best solution for you.