Losing water

I am the owner of a vinyl liner pool. I have what appears to be a unique problem and that I’ve had trouble getting a proper diagnosis or finding information about the problem. Over the last several weeks whenever the pump turns on it dumps water out the wasteline to the street for about 1 minute… some days it doesn’t periodically throughout the day. Some days it only happens when the pump initially turns on in the morning. The spider gasket has been replaced. The multi-port valve has been checked. No visible leaks on any of the lines. Any suggestions would be very welcomed. Thanks so much!!!

I guess I should also add that the filtration system appears to be in good working order. The water is crystal clear and well-balanced. We’ve checked everything that has been suggested and still at a loss