It’s not a problem, it’s just anatomy
Have you ever happened to poo and have, at the same time, the urge to pee while you’re on the toilet? But why can’t you do the opposite? If you haven’t ever thought about it, there’s an anatomic reason for that, and it’s not a problem if you were worried about it.
Our main sphincters are circular muscles that control the passage of our waste but the human body has about more than 50 sphincters and they can be voluntary and involuntary. There’s an internal and an external sphincter in our anus but the latter is under our control. The sphincter around the urethra, instead, is smaller than the one around the anus, so it’s easier to relax only this muscle when you have to urinate without relaxing the whole pelvic floor. This means you can pee without pooping at the same time.
On the other hand, when you have to poo, the relaxation of the stronger anal sphincter reduces the tension in the weaker urinary sphincter too and allows urine to pass at the same time. However, this isn’t always the case because you can poo without peeing but it’s more difficult.