If we are not able to resolve this soon, i would recommend replacing the ESC, you could then submit RMA form : https://www.modalai.com/pages/rma .
In majority of cases, the scanning script should find the ESC even if it is missing firmware or params, so I am slightly confused why this is happening. It could be a hardware issue on the ESC.
The ESC you have now is board version M0049, which is older than the current version of the ESC and is no longer in production. If you are going to request a replacement of the ESC, you will most likely receive M0134-1 which is just a newer revision (not really better or worse, the functionality is the same). https://www.modalai.com/products/voxl-esc
In order to rule our the RB5 UART issues, if you are open to continuing to debug, i would recommend making an adapter using a USB-to-serial adapter and Hirose DF13 6-pin connector, then you could use voxl-esc tools on a PC and there is more flexibility in debugging. Please let me know if you would like to explore this option.
