As the scar tissue peels off the inside of the urethra reconnection, it exposes tender spots, and some light bleeding happens. Think of a scab on your hand. The problem is that a single small drop of blood in the pot looks like the end of the world (experience speaking here).
I had debris and the random blood spot for at least two months.
But, as always, my main advice is to call your uro/surgeon with any question.