My surprise is that when the mempool gets down the first tx is executed too. I asked the owner of the wallet 3FcJ5qSBExencX5eowGJwrPBnfKX41FrXK if he received another payment and he told me checked on his ledger wallet GUI and he received it but it was tagged as double spending and then the print screen he sent me only show one TX.
It can't be a double spend; read these two words again.
Double spend. To double spend something, you have to spend the same thing twice. The two transactions are literally spending from different sources:
1st one from 3P83sWGjujgjKN2AN73Q6n52UUg9ecQyvd;
2nd one from 19mbyFd8ehSs5AyGQF1hZnS4fj6i1kRgDc.
What is happening how can he confirm the other tx ?
Both transactions have been confirmed and he has *received* the funds. You can see his balance here:
https://blockchain.info/address/3FcJ5qSBExencX5eowGJwrPBnfKX41FrXK.
Could I receive BTC from a wallet and check +6 confirmations and then lose those BTC because the same BTC were sent to another wallet with a high fee but "abandoned"
Abandon transaction is a local function. It does not, and can not, remove the transaction from the network.