As some here have mentioned before, the ATPro is somewhat sketchy on beach hunts. I have hunted beaches in Florida with mine, and grounding after EVERY dig is what I have found best do for best results. Also try to stay in one environment (dry sand, wet sand, or water) without switching back and forth.
That said, when hunting a beach, I have found that looking around before turning the machine on helps, in that you can locate where people laid out blankets, sat down, returned, etc. where people are is where the lost stuff is. Sounds redundant, but it saved time for me. Find the high tide mark, and start there.
Mine jumps around too, but those things have helped me get the most out of the machine. I hunt pro/coin as well on the beach. Ground/ground/ground and ground balance again. HTH.