I have the Sovereign GT, which is the same insides as yours, just not water proof, and I have no trouble finding coins at all. I've only used it 5 times, the first 2 times in the dry sand just to dig a lot of trash so I could get used to the sounds, the next 3 times in the wet sand. During those 3 times, I've found 1 tungsten steel ring, 2 sterling silver rings, 1 14k white gold ring with 3 diamonds, 1 platinum ring with 1 diamond, and over $15. in various change, some of it deep. I know you were asking about coins, but the reason I brought up the rings is because they were each made from a different material, yet my machine picked them up with no trouble at all, as well as all the coins. I'm thinking another detectorist was there between when you were there last time and this time, and you found something they missed or a recent drop.