I opened a topic about what may be a related discussion, at least with regard to the SERIAL_OPTIONS=7 variant not working. (Cube Orange UART Inversion & Half Duplex Problems)
At first I thought this was due to the pin output mode being set to push-pull in the hardware definition header where the reference manual wants open drain for half duplex (At least on the H7s). However, changing that during the option parsing in the UART Driver didn’t seem to make any difference.
Both the CUAV v5 and the CubeOrange have a TXS0108E over the UART lines, I assume for some form of protection. This has internal pullups which may be the source of this particular problem. Though that said the RX lines work so there may still be a software fix. One option could be to set the RX/TX swap bit in the UART register, similar to how the half-duplex mode is switched after transmission.
In the meantime an additional pulldown resistor on the line gets the telemetry working albeit somewhat precariously.