@Mastermind OK I think I'm seeing things a bit more now!
First, let's confirm, when you say LTE v2, you mean this right? https://docs.modalai.com/4G-LTE-Modems/
I ask because Tom brought up, our 5G Modem, has a real UART: https://docs.modalai.com/5G-Modems/
OK back to the question, I think what you are seeing now, if you go directly from a USB port (say LTE board or MH board) to a Flight Core, you will basically be doing what happens when you connect a Flight Core to QGC.
That USB port on FCv1/FCv2 J3 is used for QGC connections and not telemetry like we expect via a UART TELEM. (as far as I know).
So imagine if you had QGC installed on VOXL2 (this won't work!) and then you had the setup of FC straight into USB, you would then have a QGC USB connection like a host PC!
Now, if there is a USB to Serial adapter between the LTE or MH board and a Flight Core's TELEM UART port, then I would expect something similar to enumerate in LSUSB (like /dev/ttyXXX) that COULD act as a UART, and then this would be OK to try with voxl-mavlink-server, but we likely need to modify code as it expects /dev/ttyHSX at this point.
So:
voxl2 --> add on board with USB --> straight to FC J3, not gonna work as we intended
voxl2 --> add on board with USB --> USB to Serial --> to FC TELEM port, should work as intended!
We are still pressing on with the DSP UART path and will get that online anyhow ASAP (but I'm kinda slow lately so bear with me)