Remove gke cluster from Rancher caused every nodepools scaled to 0

Hi, I’ve hosted Rancher on one of my GKE clusters and imported other clusters onto it and everything worked well. Recently i’ve upgraded rancher from 2.5.8 to 2.6.2, now whenever I try to remove a cluster from rancher, every nodepools of that cluster have immediately scaled to 0 and every pods were evicted.
I’ve installed rancher using helm chart. Have anyone faced this problem before and can you tell me how to fix this since I can not do anything much to update the clusters imported on Rancher.
Many thanks !