iMac 2017 plugging in any usb device kills bluetooth (keyboard and mouse)

The bluetooth keyboard and mouse randomly disconnect whenever any usb device is plugged into the back of the machine. It's clearly not RF interference or bad battery connection on mouse and keyboard etc. Bluetooth clearly crashes as illustrated by the bluetooth icon in the top status bar. As long as nothing is plugged into the usb in the back of the computer they stay connected flawlessly. But as soon as any usb data flows across the usb hub to another device, I can get the mouse and keyboard to disconnect and bluetooth modem to crash inside a couple of minutes. The range of USB devices that causes this are pretty wide (iPhone 10, 2012 iPad, DJI Mavic drone, etc). Essentially any device that moves data across the bus is triggering it. The Apple Watch charger is the only usb device that doesn't cause the bluetooth driver to crash.

Google searching this is extremely difficult because all advice leads to noisy RF environment or poor battery connection on mouse etc. This is definitively a usb hub/bluetooth driver correlated issue as LOTS of trouble shooting has been conducted. Updating OS's over the past year and half hasn't solved this either.

Any help would be greatly appreciated.

-Ryan