Probably a bug, I've just checked it and it's ranked #20 and even clicked on it and still, it shows #20. Not a big deal though and CMC usually has some issues with the ranking of some altcoins.
Anything unusual happening today could be a joke, so don't take it as too seriously wait for April 2.
Yeah, maybe because of April fools but it has been backed to #20 again.
OH, yeah, I noticed the error has been corrected now, personally, I was of two opinions.
First was I thought maybe something happened, maybe some kind of bad news that made the project fall in rank, but I also know that if this was the reason, the news would have circulated very fast.
And secondly, I thought it would probably be a bug cus in as much as today is April fools day, and coinmarketcap is known for this kind of tricks, I don't see why they will decide to choose tron, tron is not so popular and not to many people follow the project this days, so if there were to do their April fools thing, I think they would have gone with a more popular coin or even make something new like toilet paper token... But anyways, good to see that the error has been corrected.