Didn't you already try RO WC? If you did and your test kit showed the same reading, how can that be right? There would have to be something in your tank producing N for the kit to be right. Some test kits are notoriously wrong. Look at it scientifically, Try the RO water, then if that doesn't fix it then you can rule that out. Are there any sources for copper? Meds or old plumbing??
You say the tank has cycled, but that doesn't mean it is well established. Might give it a few months, add some cheap fish which you can remove later. Then try the shrimp again.
I don't buy into the notion that shrimp can't be kept with Nitrates. Otherwise all mine would be dead, let alone thriving! I have read that plenty of people who use EI (Estimative Index) and also keep shrimp.
Keep trying and rule out one thing at a time. You will find the answer.