I've been having the same issue as Vuthy88 and have followed all the steps laid out in Move from Android to iPhone, iPad, or iPod touch, but the transfer still stalls at "Transferring... 36%" Two things happen:
1) At the beginning of the transfer, my Android device (Samsung S5) disconnects from Wi-Fi and connects to my Apple device (iPhone 7 plus) and,
2) Right at 36%, the transfer stalls, and my iPhone reads "Unable to migrate" while my Android starts receiving app notifications (despite having turned off notifications as well as mobile network connections).
Anybody else have that issue (or any solutions to fix it)?