This issue has been outstanding since we were first notified of it in December, but troubleshooting the problem required significant time and working with many customers. I want to thank ToeKneeGee, who spent many hours of uncompensated time assisting in troubleshooting.
We discovered that while Slush and some other pools are compatible with the S19, Nicehash still suffers at least partially from this issue. Therefore, we aren't able to disclose the solution at this time, but we'll be glad to help other pools resolve the issue after Nicehash has resolved it.
As always, feel free to submit a support ticket if you have questions or encounter any problems!