Weather app is not working correctly on my iPhone

If it only happens using the Weather app, two basic troubleshooting steps to perform (test after each attempt):

A) Try a "forced" restart of your device using these instructions: Put it on charge for at least half an hour, then, keeping it plugged in, use these gestures:

Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the side (power) button. Only when the Apple logo appears (it might take 10-20 seconds), release that button (ignore all other screens that might appear, the one with the "slider" to turn the device off included).

B) I would try deleting that app, restart your iPhone, then redownload/reinstall the Weather app, as per these instructions:--> Delete built-in Apple apps from your iPhone, iPad, or Apple Watch

In the issue still persists, since your iPhone is still covered by warranty, I suggest that you make an appointment (*) and have your device inspected at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> https://locate.apple.com/choose-country-region . After checking it out, they'll give you all the available options.

Regards

Giulio

(*) You can do it:

• Online:--> Genius Bar Reservation and Apple Support Options - Apple;
• Contacting a local Apple Store or AASP among the list provided above;
• Using the "Apple Store" app, available and downloadable from AppStore.

Update: There is a persisting issue about that app. Check it at the bottom of this list:--> Apple - Support - System Status