I got my OnePlus stuck in a boot loop after installing Oxygen OS. OnePlus support scheduled a remote session and managed to flash it back to stock. I was very impressed, I had assumed they would refuse the help because I had flashed it with an unofficial OS.
Oops, I got my OSs mixed up. The bootloop was after I installed LineageOS, then OnePlus flashed it back to the official OxygenOS.
Assuming the reason you're doing an RMA doesn't preclude you from reverting to OxygenOS