The behavior of ITER-like W/Cu plasma facing components under complex conditions in current tokamaks is one of the main concerns for ITER. EAST has installed a full upper W divertor with the ITER-like W/Cu monoblocks as targets since 2014. A melting failure of CuCrZr cooling tube of W/Cu monoblocks has occurred during the plasma campaigns in 2019. Due to the loss of cooling water, the leading edge-induced thermal loading can lead to the melting of both W armor and CuCrZr cooling tube, which has been confirmed by thermal simulation and analysis. With movement and migration of the melted Cu through gaps, the structure and function of the CuCrZr cooling tube for W/Cu monoblocks was severely destroyed. As a result, those failed W/Cu monoblocks had to be replaced. Such case in EAST just simulates the extreme condition of accidental loss of coolant in future devices. The melting failure of CuCrZr cooling tube was caused by operation without coolant water at largely misaligned monoblocks, which is a key lesson referenced to other tokamaks which adopt or plan to apply such type of W/Cu monoblocks.