Please look in System Preferences - Energy Saver and see what you can find. If any adjustments you make don't make a difference temporarily disconnect one of the drives from the hub and reconnect it...

I use MC210CS for this task. TP-Link Gigabit Ethernet Media Converter, Up to 1000Mbps RJ45 to 1000M Single-Mode SC Fiber (MC210CS)

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How did you decide your problem? Please write.

TP Link is not doing anything since April 2016.

For your issue, I suggest you to test again with Acrylic Wifi which is much better than inSSIDer.