It is sometimes very difficult to read a QR code with android devices using Field Service Mobile.

https://learn.microsoft.com/en-us/dynamics365/field-service/mobile-power-app-system-barcode-scanning

The device needs to be at a specific distance and angle for it to read the QR code and it can take a user 30 seconds or so to position their device properly. Please consider improving the read capability in this scenario.