For the past three months we've been experiencing lights flickering and certain electronics resetting due to voltage dips down to as low as 70 volts. This happens completely randomly regardless of new or existing loads and usually lasts a couple of seconds but can occasionally last longer and that's when electronics reset.
We have a single phase setup with two lines coming into the panel and this problem is only on one side. All circuits have now been replaced. I have mapped out all the circuits and have tested all receptacle for correct wiring. I have consulted with two electricians who haven't been able to figure this out. The dips don't cause any circuit breakers to trip. The power company has been out here a few times but of course when they come out, it doesn't happen. But just last week they installed a voltage monitor.
Amazingly this issue goes away for a few days wherever our electricity is shut down. It happened a couple of times due to storms and also when they came to install the monitoring meter and had to shut it down.
UPDATE: I was standing at the panel with my meter hooked to the fluctuating main line when I noticed another drop happening. Turned off all the main circuit breakers and voltage dropped very low and after a couple second was reading ZERO! It kept going to 15/16/30 back to 0. It was only after I turned the breakers on about 30 seconds later that the voltage was restored.