I am working on a solution to the same issue. i7 plus, ios11. Here’s what I’ve got tried. Phone had a screen replacement prior. 1) Three different aftermarket LCDs and two OEM. Same issue. 2) Backup and restore(no data restore) to fresh iOS 11. Same issue 3)prox/cam flex replacement x2 + restore. Same issue. 4) downgrade to iOS 10 - so far no freezing but the unit is still at the startup as I’m waiting for the customer to sign into iCloud. I’ll update this afternoon.