Iraq had substantially customized their Scuds, attempting to increase their range. This customization was not totally successful as it destabilized the missiles in flight.

The resultant tumbling made them highly inaccurate as to target, but it has been suggested it also made them much harder to shoot down.

Sources: https://fas.org/nuke/guide/iraq/missile/al_hussein.htm, https://en.wikipedia.org/wiki/Al_Hussein_(missile)