[Discuss] adb devices and Macbook Air/Pro old and new

[scott at ehrlichtronics.com (Scott Ehrlich)]

I am working with about 1000 Asus Nexus 7 tablets which normally get
charged/stored in charging carts that can hold 48 tablets at a time.
The carts each have a USB port under a cradle that the tablet simply
slips into on its side.   One end of a USB cable is plugged into the
USB slot just under the cradle slot, and the microUSB end plugs into
the tablet itself.

The cradles are all wired to a master USB hub within the cart with USB
cable and plug protruding out the side.

Now, using any older Macbook Pro/Air (take a MacBook Pro 1,1 for
example), and we plug the USB cable from the cart into the USB port of
this Pro, cart is plugged into the wall, all tablets are powered on
and successfully charging/connected to the cradle, have a terminal
window open and issue adb devices, all 48 tablets in that cart are
seen and can be successfully interacted with.

Same is true of a similar-vintage MacBook Air laptops.

Take a present-day MacBook Pro or Air, and try it again.   adb devices
only sees 8 devices, even if all 48 are plugged in.

We have tried this on all the carts we have and have the same results.
  We have tried the latest version of adb with the same results.

Is it an issue with adb or with the USB chips used in older vs newer
Mac laptops?

We also use some other software along with adb that is designed for
Macs, hence our reliance on Macs for doing this.

Thanks for your insights on how to break the 8 device barrier using
adb on newer Macs, if this is possible.

Scott