Why is the App losing GPS

Why does the app lose GPS signal? When O am walking down a residential road, nontall buildings. No tall trees. Nothing to obstruct the signal. It will lose GPS signal then acquire it then lose it again. Sometimes the App will stop when it loses the signal the app will stopnrhe workout. At this point the app is worthless. Which is a problem because I bought the app in good faith. So either fix the App or refund my money. Thank you fientoie attention.

What device do you use? Do you lose signal when device screen is turned off?