Come on. The existence of gravity is debatable if that's your standard.
> The current Ukrainian government asserts that the Russians invaded Crimea.
If you think this is debatable, I don't know what to tell you.
But getting back to this gravity thing... sure stuff frequently falls to the ground, but have you ever SEEN gravity itself? [Yes, this is a joke, but your point is well taken, I had a comment a bit ago about how it's hard to take some twitters comments seriously and that they often seem to just spout BS. The good news is that it's not everybody spouting BS, but it often seems like most people are.]
North Korea claimed to have found a unicorn lair (https://www.theguardian.com/world/2012/nov/30/unicorn-lair-d...), but the existence of unicorns is not in dispute.
Russia claimed to have no involvement in Crimea (later admitting they had); they also claimed the day before invading Ukraine they had no plans to do so. These are just bald-faced lies, and I think it's important to differentiate between that and "it's not possible to tell what the real truth is" scenarios.
I deeply respect Vladislav Surkov and his ability to weave a dazzling narrative. But at the end of the day most of the talking points he constructed regarding Ukraine and Donbas are complete BS.