This is a rare event ( we see hundreds of challenges won today and all of them have a key assigned ),.
We are investigating about a possible db disconnection.
It would help us to know when exactly it happened. can you provide a timestamp?
This happened to me too several times.
My guess is that the counter in the upper right corner already increases with the final blow from the player to the object,
but the game itself only registers when the object is vanished
(when the archer has died from the hit, the tree has actually fallen, the rock has shattered) - or, in the case of the beanstalk, carrying fruits.
There is a small delay between those two actions (maybe one third of a second?), and sometimes this small fragment of time is what tips the scales.
This has happened to me quite a few times. I only took a few screenshots (attached the first and last time it happened to me below with the timestamps in bottom right).
I'd say this has happened to me about 6-7 times or so in the past few days. Nothing wrong with my connection, it just doesn't seem to register sometimes and not just when it's a "buzzer beater".