I did not want to release AM:A into the world without a real-world example of it. It is not a silver bullet.
I hope I've shown you that with a minimum of terminal commands, you can restart the migration process very quickly. Without deep programming expertise but if you have tenacity and a willingness to dig deeper, you can figure out many problems.
When you figure out solutions for those problems, please report them as issues, and feel free to suggest more solutions for migration messages, I will make sure they are merged and released swiftly.
Finally, for sites with so much data that they need hours or even days to migrate: that's what the "Refresh" tab at the top right is for: to only migrate new and changed rows.
P.S.: I applied the conclusions from my review above (pushing me slightly past the hour). Only the 3 irrelevant "Site configuration" rows are left: