I have noticed this too. I have been playing it quite a bit. There is no reason to have one unique solution per board though.

Some thoughts:

Insane is not harder than Hard. Often times the opposite seems true.

Scratch mode auto-committing on win is a bit too nice.

Dark mode is whack, terrible contrast.

I would like a player profile with stats and so on.

Random Insane seems to play like one of 50 levels. I recognize them often. Seems not so with hard. Now I just enter the puzzle IDs in turn...

Some puzzles seem to have no prior solutions as my time is often exactly the global average.

I would like to know how many solved a puzzle. Also if I did.

Overall great job and I love this. I would like it to be an app or something that can be bookmarked.