Do you add any products to the water? The mystery plague in my gf's tank was that she was adding a little bit of bac booster every time she did a water change, which apparently has some kind of chemical that is lethal to inverts.
Your ammonia/nitrite/nitrate/pH/temp readings are fine if they are accurate. There has to be something else in the water that is killing your inverts. The only two sources are your tap and yourself, so first take a look at your tap. Does the water smell, or do you have very old plumbing? Also, take a look at your water company's website to see if there have been any flushings or something out of the ordinary done to your water recently.
Next start checking your end of the table. Did you/anyone else use the bucket and rinse it with soap? What kind of water products are you adding? Does your water have any kind of odor that is different from the water straight from the tap?
The last thing I can think of is that some foods contain copper sulfate as a preservative. Copper is lethal to inverts, but the concentration is (should) be so low that it is negligible. You could feed boiled zucchinis just to be safe, but I doubt this is whats killing your shrimp.
I hope it works out for you. Cherry shrimp are hardy little things so there has to be something spiked in your water. :frog: