You can use ovm_utils to create/modify the cpu groups. I did that and created cpu groups for my two server pools and moved all VM servers into their specific cpu group. After that migrating using OVMM wasn't an issue anymore.
If you don't have already installed ovm_utils I strongly recommend to do so - those are really useful tools to have at hand.
You got experience like me, could you try to do this? if working fine, please kindly let me know because now I try to migrate and success by command line on VM Server but during migration is time out so long not like on Oracle VM Manager.