iPhone Won’t Show Navigation Prompts While Multitasking

When you veer away from the maps app while navigating, maps will show on-screen prompts that tell you what street to turn on/when to turn. This feature only works about 25% of the time and I can’t figure out why. For example, when I’m on FaceTime and navigating, I hear a ding that signals I need to turn, but I seldom get any on-screen prompt. I then have to switch back and forth between the maps app and FaceTime constantly.

Is there a fix for this, or something I’m missing?