I don't know if it's bugged, but the game doesn't count most of the light switches in the house towards the total. I got to 6/7 but there were no more, so I could not progress.
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The quest is to investigate upstairs, and so only upstairs light switches count. Sometimes people miss the laundry room which is on the wall on the backside of the stairs. Sometimes people also don't fully go into the attic and trigger that event, which is required for the attic light switch to register.