PX4 Cube Black/Purple Won't Boot if mavlink is streaming into TELEM1

I’m running into the following issue where a Cube Black won’t boot if there is mavlink data streaming into TELEM1 (TELEM4, ttyS6 also has this issue - haven’t tested others). Does anyone have any experience seeing this?

Is there something with the bootloader hanging up if data is coming in over UART?