Louis II's death is contested because very little information left about it giving way of much speculation, which started right after the event. The story is that he drowned a river Csele, fell down the horse, or stuck in the bog or the horse fell back while climbed the bank, in short: it was an accident. It was pointed out that it's not a river but a brook 'bout the depth of soup bowl, and this is very suspicious. Also some story was about his body was recovered without his armor, and had wounds on him, must have been killed then they lied about their death or something like that. Then the explanation came that the brook was flooding and yaddi-yaddi-yadda. Then came the conspiracies who wanted him killed and why, looking for motive (well the Crown was enough motive) and stuff liek that.
For about one and a half century now historically it have been well established he drowned in the brook Csele. Now as I googled his death I found bunch of articles saying: "the legend debunked! researchers found the king didn't drown in the Csele!" - what a turn! Did he really was murdered? No. The sensation is that now they say he drowned in a smaller branch of the Danube. While this result might be valuable in the research to locate the site of the clash, the idea, no matter how probable is, does not offer much in the topic, just shows how established the motif of drowning in the historiography (which very well might be just a trope from those times).