Find my iPhone and Approximate Location

We are having an intermittent problem with the results of the "Find my iPhone" app.

One of our kids is "findable" (iPhone 13 pro-max) nearly 100% of the time, regardless of whether they are inside a building, and no matter where they go with regard to signal strength! Rarely is a precise location Ever not available. By contrast, the other one of our kids' phone (iPhone 12 pro-max) only will show a precise location about 50-60% of the time. I've factored-in possibly being inside buildings, periodically out of range of a good enough signal, etc... The thing is that I have been with the kid with the "not-so-precise" phone, and can sometimes see them via the app, and sometimes not whether they are in any of these types of places. Any ideas?

Thanks,

Robert