I don't understand why I received this task while it was running on another host.
The task has been validated two times.
I also don't understand why I haven't received any bonus while I sent the result in less than 24 hours.

I don't understand why I received this task while it was running on another host.

Because the 1st host did not sent back the result within the deadline of 5 days.

The task has been validated two times.

In reality the 1st result is used, the 2nd result is validated only to be able to grant credit for it.

I also don't understand why I haven't received any bonus while I sent the result in less than 24 hours.

Because the credit is assigned to the workunit (not to the task), when the first result is returned, based on the turnaround time of the task. The 1st host returned the result before your host did, but after any bonus deadlines of that task therefore the standard credit has been assigned to the workunit. Later your host could not assign the credit amount with bonus to the workunit, so your host received the same (basic) credit amount.
This is a known error in the workflow of the bonus assignment, but there's no manpower to fix it. It happens from time to time with every fast host.
It's annoying, but we have to deal with it.

Thank you for your explanation, it's much clearer now.