[ovirt-users] Cluster compatibility 4.1 to 4.2 upgrade

Dear Listmember, I've just upgrade to my ovirt-hosted-engine from 4.1 to 4.2.3. It was successful, but it saw " Data Center XYZ compatibility version is 4.1, which is lower than latest engine version 4.2. Please upgrade your Data Center to latest version to successfully finish upgrade of your setup." My first question is that, it need to do BEFORE or AFTER the node upgrades? I haven't upgrade my nodes yet, because after upgrade the live migration does not work with some VMs. It seems only affected those VMs that's have big (>8GB ) memory. It counting to 99 percent and after a while just stopped. At this moment I can't stop my affected, productive VMs, so I can't do the upgrade of nodes. I just wondering, if i do the upgrade to 4.2 , that's maybe repair my the live migration function? What can I do? Centos 7.4, NFS storage, 4 nodes, Hyperconverged hosted engine. Thanks in advance, Tibor