This could happen in some cases:
1. Your investment was last in the row compliting the masternode. Half of the investment has been already included in the masternode. The other half is waiting for the new masternode to complete.
2. You got a share sold by another investor for a part of your investment. The other part is included in a new node.
Please note that in the second case if the investmenent left is less than minimum investment it is returned back to your wallet.
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