Hi, Username8736,
Thanks for visiting the Apple Support Communities. It sounds like you have multiple iPhone devices set up with the Find My feature, but one in particular does not update its location like the others. We'd be happy to help!
First, make sure that iPhone has the latest version of iOS installed: Update your iPhone, iPad, or iPod touch - Apple Support
We also encourage you to ensure your Location Services settings are enabled for your device: Turn Location Services and GPS on or off on your iPhone, iPad, or iPod touch - Apple Support
You can also use the Apple Support article If Find My is offline or not working - Apple Support for additional troubleshooting.
If you still need help, please respond back and let us know if this occurs while the iPhone is on cellular data only, Wi-Fi only, or both.
Best!