Yesterday I destroyed a guy just after the attack protection, and when my recyclers arrived, the metal en krypto was gone, 2min after attack, there's nobody arround him. And no astero.. 
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It maybe worth having a scan of the area and see who has a Roid close by. If someone saw you fly and had time to time things right they could have easily let you do the hard work while they took the reward
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Because of the rubble field event, bigger players send their recycler often to planets in the hope of rubble fields appearing.
Perhaps one of this stole ur field.
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Maybe another player attacked the same planet after you but timed his recyclers to land just after his attack? Thus he had the right number of recyclers to scoop up the rubble.
Alternatively, could your target have come online shortly after the attack and recycled the rubble himself? Perhaps an escape flight or recycle mission returned between your attack and recycle flights giving him the ships needed to scoop up the rubble in under a minute?
