USB devices intermittently disconnecting
Disclaimer: this is an answer under construction.

Open the  &gt; About This Mac &gt; System Report...,
select Hardware &gt; USB,
and open every small ▼.

Select the USB bus where is connected your USB hub, and enlarge the
lower part of the window to have a complete vue of all your USB equipments.

Make a screen capture: commandshift4, space, select the USB map window and click.
You will get something like:

Include this screen capture within your OQ (original question).

Verify that the sum of the Current Required (mA) of all the equipments
connected to the same internal USB hub don't exceed the Current Available (mA) for the hub. This value might be different depending on the USB port available outside and what is already connected on it internally.

As a basic simple rule, avoid the external USB port which is on the bus where is connected the FaceTime HD camera (Current Required (mA) = 500 mA).
For example, on a MacBook Pro, I discovered through trials that my FaceTime HD camera is on the bus with the USB external port nearest from the front.

To check this hidden cabling, just use your external mouse.

Connect it on port nearest from the front. Hit commandR in System Report... to refresh the USB connection information.
Note on which bus is this external USB port.

Repeat the same operation for port farthest from the front.