Doubt support will be able to resolve this and I'm not holding my breath for there to be a firmware update to address it either considering how long it's been a thing.
I had exactly the same results with Axe I/O (non usb powered) on latest firmware doing a loopback test (-20dB lower)
I've ended up using Line out and dedicated re-amp box, but you could run through a DAW and adjust the levels to amp out that way.
