After some googling, I suggest this could be radio being busted due to incorrect power supply handling. Turns out, there is a pitfall.This might be worth reading: https://community.st.com/s/question/0D53W000011WcYkSAK/smps-danger-the-device-may-be-de...

I have a custom project on a custom board in my case, but the problem seems totally same, SUBGHZSPI_Transmit returns timeout. I've broken several chips and feeling hesitant to flash another one.

Any update anyone? I'm having similiar issue, timeout waiting for RXNE flag. The transceiver seems to be somehow off.