I'm not sure if you use kernel-power, but I experienced a lot of graphical corruption when the voltages were too low. Perhaps that's something to check out before dismantling the phone.
If you can SSH to it, it's worth checking the output of dmesg for:
[ 100.487518] HWRecoveryResetSGX: SGX Hardware Recovery triggered
I was regularly getting those whilst seeing the corruption. After returning to default voltages all has been good.