[spiderplant]

This is usually caused by infra-red interference in the room. As it only happens at night, it's likely to be caused by the lighting in the room. Do you have energy-saving bulbs? Some of these, especially older ones, send out IR signals that interfere with the signals from remotes. You can easily check if this is the cause by turning the lights out. You might need to replace the bulbs or move the STB so it isn't directly in the light.

ps Welcome to the forum!