The message you get when running /debug start is

Started 10 second tick profiling (use '/debug stop' to stop early)

This is copied a bit too much from the /perf start message, as the /debug start command doesn't automatically stop after 10 seconds. You need to stop it yourself. I expected the message to be

Started tick profiling (use '/debug stop' to stop early)

Alternatively, the message could be the intended behavior and in that case the command's implementation should be fixed to match this.