The puzzles in this game are extremely hard. I had several testers and they are all solvable... In the case of symmetry, There may be a fundamental misunderstanding that you are operating under, such as that they are pairs of matching numbers. For the failings of these puzzles, I do think I managed to stay to the philosophy that successfully completing each step gives a coherent output. This ties into what you're saying with the different answers (which you are right about) that riddles can have, and while several might have those multiple answers, there is actually a pattern that shaves that number back down again.
Of course, I'm not gloating that the puzzles are hard and that I have a very big brain. After all, it's not difficult to make a very hard puzzle... it's trivially easy to do. Making a hard puzzle that's fun? That's the big brain thing and as you point out... A lot of these are not successes by that metric. It is a sliding scale and the intended (very niche) audience did very much enjoy these, but that enjoyment was at the cost of accessibility to almost everyone. I think the next time I do puzzles... I'll do something a little easier, both in terms of challenge and required design effort.