Migration Assistant failure with MBA to MB.

Received the new MacBook and followed the instructions to use migration assistant to move my data from my MBA to the new MB. Both computers could recognize each other, but the migration failed within 30 seconds of clicking the continue button. MA never got to the point where it asked what I wanted to migrate. The error was: "Migration Assistant has unexpectedly quit. Please try later." Trying at least a dozen times over the next five hours with no luck - exactly same results. Got Apple Tech help up to Level 2 support. They suspected it was a bad OS build, so they had me erase the OS and reload it from scratch. That took another hour. Re-tried migration assistant, but got exactly same result as before. Level 2 doesn't know what's going wrong. Cannot migrate with cable because the MB has only the one USB-C port and Migration Assistant requires that the computers be attached to power, not battery. The USB-C multiport (which would allow data and power transfer) is not available from Apple yet, so WIFI migration is the only option right now. Unfortunately had to return the MacBook. I can't afford the time drag in trying to figure out this problem. If anyone else has had this problem and been able to resolve it, please let me know. I might re-order the MacBook if I knew the problem was solvable.