I got a notice in the NetApp community that this is caused by the bug 2668244 and a fix should be targeted for ESXi 7.0 U2. There is a problem with NFS file locking that slows down the migration of VMs on VVOL datastores.

So i tested the december beta:

host1 = ESXi 7.0.1 (U1c)
host2 = ESXi 7.0.2 (december beta)

When i'm doing a vmotion from host1 to host2, the vmotion takes only 5 sec.

But when going back from host2 to host1 then it takes 40sec and the VM freezes the most time.

So i was hitting the bug and the bug is fixed in the next update version...