IPhone 6 Plus and 7 locking up
you could try downgrading to an older version of ios. you would need to put the device into what is called DFU mode or recovery mode, see here:
https://www.youtube.com/watch?v=15qaTA4lQPc

you will also need to download the version of ios you want from here 
https://ipsw.me/

once downloaded, put your device into dfu mode, open itunes, hold shift and click restore, browse to where you downloaded the firmware file and install it