You are right about the stale shares of nanominer. But for some reason gminer is not producing an accepted share for any of my 390's under smos. It may be related to opencl version 18.20 or it needs root access, I don't know. I can't test now under hiveos, where the opencl is 19.20. Any suggestions?
I use amd pro 19.50 and 20.30 drivers in ubuntu and hive. Try them.