I am absolutely baffled by a 4x4 Rubik's cube I'm working on!
Having arrived at an almost solved puzzle bar one flipped corner, I concluded it was assembled incorrectly after reading about similar situations. (Later told by friend their kids had had it fall apart and reassemble one day)
I got to disassembly and noticed it is nothing like any of the cubes in tutorials, the corner pieces seem to be fixed to the centre ball, and not removable without disassembly of the centre ball.
I concluded the only solution was to alter the tiles on the corner piece which worked fine, and reassembled the cube in its solved state
I mixed it up then got to solving and arrived at a peculiar situation that didn't seem to match any cases the tutorial was suggesting is possible, so eventually went to an online solver and thoroughly entered my scenario several times, each time getting back an impossible solve error - cube is assembled incorrectly.
So my question is..! How is it possible that a cube that was solved, is now unsolvable regardless of how it is assembled? Surely it would be feasible to backtrack in theory and arrive solved.. I'm quite sure I haven't forced any pieces into illegal manoeuvres, no great speed or force happening.
Is there an incorrect way to assemble a solved 4x4 cube?
Thanks in advance! XD.