The wind will blow the sleeve off the hook if it is not secured properly.  Use a ziptie or closed clip to secure the sleeve to the hanger

      Screws holding the hook to the wall can break.  The Hook itself can break, or the shepards hook is not secured in the ground properly. Use strong       construction screws, the type used to build decks.  Often the decorative screws that are supplied with hooks are weak.

      Not having outdoor rated power connections/cords. This can cause the GFCI to trip frequently, leaving the pump off.

      When you have large plants, they use a lot of water.  Keep an eye on the level of nutirent solution.