A bp shouldn't get scale rot if it is being properly cared for. I believe it is usually caused by being in damp and/or dirty substrate.

Mouth rot is usually a complication of something else. Like if the inside of the mouth gets damaged from swallowing substrate or getting bit/scratched by a rat. I think I've heard that the germs from mouth rot and RIs can kinda go back & forth so one can cause the other, although I'm not 100% sure of that.

That brings us to the most likely health issue. RI. Respiratory infection. Most often caused by "opportunistic" germs, which means they are always present in low numbers, but can get out of control when an animal is vulnerable. Like if your heat source goes out and the snake gets chilled, or something of that sort. But RIs also show up at times no one knows why. Symptoms to look out for are wheezing, whistling, popping, or any other weird sounds when breathing, although these sounds can be caused by other things too so no need to panic at the first sign. You may also notice, especially as an RI gets more advanced, sitting with the mouth open and/or the head raised (presumably makes it easier for them to breathe). And you may notice mucus in the mouth.

Mites are another common problem, but they have to come from somewhere (like you handled a snake at a pet store that had mites, and a mite rode home on you). Most likely the first thing you'll notice is your snake soaking more than normal. You can also see the mites on the snake, but they are easy to miss when the numbers are small.

Properly cared for BPs don't have health problems very often.