It's actually working as intended, it's to compensate for SE adjusting the amount of items you can set in a personal house. They increased the amount of items you can set inside and outside a FC or personal house, but the trade off is if you exceed the original limit of interactive items like lights, the game's client may randomly make certain furnishings/items appear and disappear briefly.

This was stated in the 4.0 patch notes on the Lodestone (sadly I cannot link to it as the Lodestone is down for maintenance at the moment), as a natural part of the game so sadly there is no way around this I'm afraid, except reduce the amount of interactive furnishings you have in your house if it's too annoying for you.