Two identical timers on iPhone

When you set a timer it does not delete previous timers you have set, so if you previously set a 30 minute timer that has expired, then set a new timer for 30 minutes you will have 2 30 minute timers, on current and one historical. This is a relatively new feature so you can reuse timers that you have used previously, without having to create a new timer. If you open the Clock app and tap on Timers you will see all of your recent timers.

Yes, it does, because it is a recent timer. It isn’t running, it is just a placeholder. When your new timer completes it will disappear, and leave just the recent timer.

How are you setting the timer?