I haven't had that bug. But it has happened to me more than once that I've done all three puzzles and then only had two in my stats. It annoyed me when the one that disappeared was a successful puzzle, but at least I could do another puzzle.
Maybe you can report it to chess.com, so they can correct the bug. That's how you improve software, isn't it?
I did the three puzzles that are given to you every day, got them all correct but when I went to look at my stats it showed I got the first of the three wrong; I even took the time to find all the moves before starting the first move.
The puzzle was actually fairly easy, but I wanted to work out the entire solution before moving. It's a mating net situation.
I'm very disappointed.