Try check this aswell.
If the adhesive battery tape snaps off whilst being pulled out, the iTech may use alcohol to release the tape. If the screen is still connected, the alcohol may seep under the screen connectors. Although most of the alcohol will evaporate, the alcohol under the screen connectors will take longer to disappear. This will cause the screen to flicker and may even damage the circuit board as the alcohol is causing mini shorts.
Remove the screen connectors to ensure there is no alcohol underneath them. Additionally when using alcohol to dislodge the battery adhesive tape, dip the card / tool in to the alcohol as apposed to squirting alcohol in to the phone or under the battery.
This would explain why switching the phone on and off several times may cause the issue to go away as the alcohol evaporates.