I can see right away that the solution requires casting Divine Spirit and Vivid Nightmares on Lab Subjects to get extra copies of both, but the spells don’t carry over to the copied Lab Subject. To be more precise, the spell effect carries over (the copy displays Divine Health as an active buff when you hover on it) but when it dies the active buff isn’t returned to your hand - only the original Lab Subject returns it. It recognizes the minion as having a buff without recognizing that buff as a spell that was cast on the minion.
I looked up tutorials because I thought I was going crazy, but it appears that the interaction was broken at some point. I came across this exact issue in another puzzle, but was able to find another solution. However, in this case, since you can’t get the extra copies of spells needed to beat it, the puzzle is broken and impossible to complete.