this DOES NOT WORK FOR ZCASH. Even if it worked - this is PREFERRED diff, but not the static.
Note: Your miner may sometimes work with lower or higher difficulty since the difficultly you set is only a preferred difficulty and the actual difficulty depends on the current orders at NiceHash. This is completely normal.
also 5.0 version does not support nicehash for devfee. Have you set static diff for devfee pools?