I agree with gt_addict, we have noticed the pi's have a hard time with excessive bandwidth. I have a few pi4's on order to see if it makes a difference. they support full USB 3.0 though, so that may be a completely different challenge.
@Gage-Miner, when you run one of your R606's individually, what is your frequency and your hash rate?
Yeah, just tested my r606's on my linux desktop on usb 3.0 as I'm looking at picking up an Odroid XU4. Problem with it, 1 usb 2.0 and 2 usb 3.0 ports. On my desktop, once I plugged the r606 into a 3.0 port, they zombied out the first pass. 2nd try, they gave me read / write errors. And when this occurred, it screwed up all usb ports so would have to reboot the box to correct

Is this an issue with the r606 themselves for usb 3.0 or is this software related?