I have a FTP and have seen similar communications "dropouts" , i say dropout because i have experienced both driver related issues and comms issues due to the USB interface. The correct recent online downloaded drivers in most cases solved any issues with software, but the usb port(on the pc-laptop, not on the FTP) and the cable thats used i have found to be the majority of problems iv had, iv put it down to noise on the usb bus most of the time, ie. having a pile of usb devices or even worse, an external usb hub all plugged in at the same time. some usb ports on pcs also have different controllers on the mainboard and thus operate at different speeds so perhaps try a different port, also if one device causes a problem it can cause all devices on the bus to operate at lower throughput, and length of cable is also a necessary spec with usb again due to noise(and resistance) and this occurs even with powered devices.
So just to out-rule any of this, maybe try getting a shorter and quality usb lead, removing any unnecessary usb devices(especially external hubs) from the pc-laptop and avoid using the usb ports on the front of a PC, use one in the rear when possible.