Yeah, XMODEM... I had to implement YMODEM for a client of the company I work with a few months ago... Over BLE. It is every bit as bad as it sounds like.
It is more common that you imagine. In my case, the story is that some people have literally been porting the same C code base on multiple computers first, and embedded devices later, since the late '80s. Given their lead engineer is literally 80 years old now, the client once again slap YMODEM on their latest device, which uses BLE to literally emulate a good old serial port and pass data on it using YMODEM. It sucks, hard. They were quite puzzled about why it ran so badly, and I didn't have the heart to tell them it was because the whole thing was incredibly idiotic.