Ideas
While doing challenges around Gullcrest, I did the challenge called Holy Huck. Upon completing all the goals besides the Co-Op one, the game did not play the Shut It Down sound, nor did it display the text. It just said "Complete" and played the audio for I guess only doing one of the goals?
On the map afterwards, all the goals are lit up except for Best Slam Score, which has no value next to it. I have a feeling this is related to it having 6 goals, which is the most of any challenge in the game as far as I'm aware. I think the game doesn't handle that properly.
Attached is a video of me doing the goal and having the above behavior be present.
Same problem as me I just did it today and the same thing has happened, the slam distance doesn't say complete after nailing the challange.