It looks like a known issue according to the Gminer thread. It works fine to mine on Nicehash for a while, but then you run into errors.
But is it possible for AM to report/use 'total_accepted_shares' when there is no accepted per device?
gminer's /stat:
{"uptime":59,"server":"stratum://beam.usa.nicehash.com:3370","user": "X.Y","algorithm":"Equihash 150,5 \"Beam-PoW\"","electricity":0.004,"total_accepted_shares":14,"total_rejected_shares":0,"devices":[{"gpu_id":0,"cuda_id":0,"bus_id":"0000:01:00.0","name":"EVGA GeForce GTX 1080 Ti 11GB","speed":31,"temperature":73,"temperature_limit":90,"power_usage":256}],"speedRatePrecision":0,"speedUnit":"Sol/s","powerUnit":"Sol/W"}