Pokémon Masters EX has confirmed an in-game issue affecting weather, terrain, and zone effects. When a non-EX version of one of these effects is active, introducing the same type of EX version may incorrectly extend its duration. The development team has acknowledged the bug and is working on a fix. Players are advised to be aware of the issue during battles until an update is released. DeNA plans to share more details once the correction is implemented to ensure fair and consistent gameplay for all Trainers.
Source: Official Pokémon Masters EX site
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