If the Ethernet cable is not connected at the time the LwIP_DHCP_task is running, no IP address can received after reconnect the cable.
Does anyone has any idea how to solve it?

I don't know of any FreeRTOS examples that use DHCP. I suggest trying the lwIP mailing list. It is very active and somebody will be able to help. Please report back here when you have an answer.

Change following in ETHIsr,c or equivalent,

//while (!(PHY_MR1_ANEGC & EthernetPHYRead(ETHBase[0], PHY_MR1)))
//;
if(PHY_MR1_ANEGC & EthernetPHYRead(ETHBase[0], PHY_MR1))
{