1A per USB port may not be enough to run them at 500
The Sidehack USB hub provides up to 6A per port (shared between two ports)
Its a 120W hub with 10 ports, im only populating 3 ports for F + cooling fan. they are pretty steady at 550Mhz when a single hub is plugged to PC but as soon as i plug in a second hub to PC, the frequencies begin to flutter & the Fs on the 2nd hub wouldnt go past 300Mhz while affecting the Fs on the first Hub causing it to drop also ...
Yeah the 10 port 120W hub is better than the 7port one I thought you had, but its still only 2.1A per port. I've had no end of trouble testing different hubs and only the Gekkoscience ones work reliably in my experience.
The only other trouble I have had was when I didn't have enough cpu grunt to drive three sticks. I was using a lowly Pi1 and it just couldn't drive more than one stick at full speed.