I think there's one situation where the border was defined by the river but then the river moved, and some Americans ended up on the Mexican side of the river. I'm not sure if this is an active border dispute or not.
I think there are some semi active disputes going about the possibility that some American water management activities in the watershed may cause the river to shift more. For reference, the headwaters of the Rio Grande are deeper into US territory, not on the border
Continental drift in its current form was theorised by Alfred Wegener. Wegener was a citizen of the German empire. Empires were invented by Rome. Rome shares two letters with Race. Race is a social construct that allows for racism. Therefore all Mexicans who have allowed their border to continentally drift away from Merica are racist.