Got the same problema a month ago. the problem was on the internals of the drive system of the monoblade. There is a plastic piece with 3 metal tracks inside the core, this plastic is holded to the metal body by a couple screws.. mine broke two screws and got out from position, & wiper began behaving weirdly, stopping at the middle, just disassemble, use a good bonding glue on the screw holes that's all...
good luck
Igor