I won't guess, what exactly is going on there.. but according to your description it looks like, you've enabled some direct monitoring of inputs at Focusrite Control, so as soon as you start playing some signal to physical output, it will return back to physical input from your outboard and then it's immediately routed back to the same output.
Try open Focusrite control, open its File menu and find the "Direct routing" preset. This will essentially defeats any direct routing at low latency DSP mixer and assign physical I/Os just to DAW inputs and outputs. That's what I would try as first step.

You can also check Focusrite Control user guide with more in-depth explanation of its functionality.. It's worthwhile read for any owner.
https://global.focusrite.com/downloa...=Clarett+8PreX

Michal