A vMotion from host A to host B fails and is stuck at 20%. Soon after the start of the vMotion, at the destination host B the datastore becomes inaccessible as reported by the vSphere client.
This happens at ESXi 6.5.
the MTU size of the VMkernel which is used for the NFS connection has a MTU of 9000 while the distributed switch has a MTU of 1500.
Solution: make sure MTU sizes are the same on virtual switch, vmkernel, physical switch and storage controller.