Some puzzles are showing problems … some cards are doing more damage than normal, other characters have more life than ideal … I saw some videos on the internet, where a character’s life is shorter, but in the game she is bigger.
You may want to be more precise regarding which puzzle you are referring to. Currently, there are problems with a few of the puzzles because some Priest cards were nerfed when patch 17.0 came out (Holy Smithe and Power Word: Shield). This is known and a fix is upcoming, no release date announced at this point.
However, I believe you are referring to a much older bug. When the Puzzle Lab was first released, there was a bug which caused some of the opponents in the Lethal puzzles to have less health than was intended. This was fixed a few weeks later, but a lot of the older video guides were recorded before the fix, so they show a different solution than was intended. So if you are stuck in a puzzle which is NOT one of these three, then there IS a solution, look harder (or find another guide on the Internet):
[Astromancer Arwyn’s Mirror Puzzle] #6 and [Dr. Boom’s Lethal Puzzles] #3 and #4 are the ones currently impossible to beat,
Boom’s Lethal Puzzle #3 is actually still possible. The most commonly reported method in guides won’t work but there are other methods which get the draw by healing with the Cleric - including one I stumbled into that only recently became possible because PW:S costs 0.
Unfortunately I’m pretty sure #4 is still unsolvable, since it has much less tolerance.