If there were non-broadcasted transactions, shouldn't they be able to see the UTXOs inside the wallet? OP claims that the private keys lead to empty addresses.
The transaction in question is coinbase.
I think OP have a fake wallet showing he has mined bitcoin. Once he did reindex, the transaction status changed to "
0/unconfirmed, not in memory pool" which means that the transaction was neither found in the blockchain nor in OP's own mempool.