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This is caused by the multifunction switch itself. The switch works off a resistive multiplex system where it receives a reference voltage and puts it through a series of resistors for the different switch positions. The return voltage is read by the instrument cluster which then determines switch position based and the voltage. An incorrect return voltage from the switch will either cause the wrong side to flash when you turn the turn signals on (this is pretty common with a failed switch), or if the voltage is out of a normal window by far enough it may not even turn the turn signals on at all.