Puzzles ending before checkmate.
Agreed, not seeing the checkmate puzzle is a lot a frustration. Especially as a beginner. I have played checkmates puzzle without being to checkmate when replaying the situation vs computer. It definitely feels like the puzzle is not helping in gaining greater knowledge. Rather the contrary at times.
ps. not sure I understand @SacrifycedStoat's point.
Not sure if this is the right place to post this, but...
I've encountered a lot of puzzles that are checkmate puzzles, but I get two or three moves in and it says the puzzle is solved before mate is fully delivered. It can be confusing and a little bit dissatisfying because 1. You don't get to see the checkmate play out and 2. If you're not mindful it can give the impression that you've delivered mate when you haven't.
I think any puzzle that involves a mating pattern should allow the user to see it to its conclusion.