This Ability effect may be in need of research. Reason:If a Pokémon whose Ability has already been suppressed by Gastro Acid obtains an Ability Shield, is the Ability suppression removed permanently (i.e. even if the Pokémon loses the Ability Shield), temporarily (i.e. only while holding the Ability Shield), or does it remain in place? You can discuss this on the talk page.
If a Pokémon with an Ability Shield transforms into another Pokémon (either by using the move Transform or using the Ability Imposter) it will still copy the opponent's Ability. This copied Ability will then be protected.