Devices on adb are fluctuating
I've had the same problem when trying to use ADB on lots of devices on one hub. ADB uses a lot of the available USB bandwidth, so when many devices are on one hub, they can't all get the bandwidth they need. There are several suggestions you might try:-


Use ADB over the network instead of USB. If you don't know how to enable this on the device, there are a few apps to help you. Once it's enabled on the device, use adb connect ip.ip.ip.ip:port from the development machine.
Make sure the cables are plugged into a USB 2.0 port, not USB 1.1. USB 3.0 is even better if the development machine supports it. The different versions of USB are all compatible, but later versions have much more bandwidth.
Try a better hub. Cheap hubs are designed for plugging a USB storage device alongside a keyboard and mouse, and don't cope well with high bandwidth use. A professional-level USB hub will do a much better job - but it still might not be enough to connect all your ADB devices at once.