Hi Ryan,
I have the same problem.
After a screen replacement on my iPad Air:
1. the lock function with original Apple iPad Air Smart Cover don't work;
2. the lock function with the power button don't work;
3. the lock function with Assistive Touch don't work!!!
The flex power cable is undamaged.
I'm going crazy..... so, Ryan, have you fixed your issue? And if you fixed it, how?
Thanks in advance
Mauro