Use stratum also for decred.
Replace
-dpool http://dcr.suprnova.cc:9112 with
-dpool stratum+tcp://dcr.suprnova.cc:2252The rejects will drop to 1-3%

And You have to wait for almost 24h for DCR confirmation.
Thanks that made a difference btw can this Cannot parse JSON! be ignored?
ETH: Stratum - Connected
DCR: Stratum - Connected
Need to check DAG file (epoch #46), starting...
ETH: Authorized
Cannot parse JSON!
DCR: Authorized
DAG file (epoch #46) is ok.
Need to check next DAG file (epoch #47) in back
Applying DAG epoch #46 for GPU #0
Create GPU buffer for GPU #0
Applying DAG epoch #46 for GPU #0 done
Applying DAG epoch #46 for GPU #1
Create GPU buffer for GPU #1
Applying DAG epoch #46 for GPU #1 done
DAG file (epoch #47) is ok.