Slow transfer speed

NetDrive version: 3
Windows/ Pro 10
Transfering file from Synology nas to Windows explorer PC only gets max speed of 355ks
Have a 50mps internet connection on the win pc & 100mbs on the nas.
Driving me mad, There is no throttling by the either ISP, What am I missing ?
Hoping someone can point me in the right direction
Regards
Peter