Reminds me of trying to do IoT stuff in hospitals before IoT was a thing.
Send exactly one 205 byte packet. How do you really know? I can see it go out on a scope. And the other end receives a packet with bytes 0-56. Then another packet with bytes 142-204. Finally a packet a 200ms later with bytes 57-141.
FfffFFFFffff You!
If only there was some sort of User Datagram Protocol where you could send specifically tuned packets like this.
Things like these make me cry
If you were using TCP, then this is absolutely normal and expected behavior. It is a stream protocol, not packet/message based.