What do see most often in sluices and highbankers (permit required)? Too much water too fast... dial it down! If you doubt the flow, test the tailings directly off the end of the sluice. I'll bet I could "cleanup" off the tailings and catch pans on just about every operation running in the Hills!
As critical as sluice box setup is cleanup. You need to break the flow of the creek by lifting the flare end of the sluice first. You can then proceed with cleanup. If you do not lift the flare end first, it’s easy to dump what was in the flare right back into the creek or disturb the riffles where your gold is probably resting.