I have been refurbishing lcds and have had this problem recently come up with iphones. It could be a couple issues. Either your connectors are not properly seated or a static charge has built. This static charge occurs when seperating the lcd from the glass. There is a white line of special paste at the top of the lcd that prevents static. This gets damaged during the process. If not reapplied it will allow the lcd and even the entire phone to build a static charge.
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