You will lose the pro version when you uninstall the app or reset your Android if you upgraded to the pro version by redeeming a public voucher. This is not the case if you upgrade by purchasing or redeeming private voucher.
However, private voucher is tied to the device, not your Google account. If you upgrade by redeeming private voucher and reinstall Learn Quran Tajwid, you have to use the same device and have Internet connection when opening the app to allow the re-upgrade process.
On the contrary, purchase is tied to your Google account, not your device.