Pokémon Masters EX has acknowledged an issue where, under certain conditions, items that were not meant to be distributed may appear in the Temp Storage section of the Present Box. Players may also see an error message when trying to collect those items. According to the notice, the items are not actually obtainable and the error does not affect normal gameplay or account data. The team is aware of the problem and is working on a fix. In the meantime, players are advised to ignore the affected items if they appear. While minor, the clarification helps clear up confusion for anyone who spotted unexpected rewards.
Source: Official Pokémon Masters EX site
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