Unfortunately, since the Pokémon has such a low spawn rate, you may need to go back and forth until it spawns. Once it does, though, you’ll want to immediately start your encounter with it before it despawns, as it may be some time before you find it again.
If Sandy Shocks doesn’t spawn in the area right away, you may want to travel to a different location in Area Zero and then return to it to see if the Pokémon has spawned.
Source: https://www.distractify.com/p/where-to-find-sandy-shocks-pokemon-scarlet