Please follow the troubleshooting steps below.
1. Update MobileTrans to the latest version:
2. Uninstall the connector in the Android phone;
3. Restart the Android device and computer;
4. Replace the USB data cable and reconnect the device;
5. Set Android to not lock the screen and the screen is always on (some mobile phones will end the process if the screen goes black);
6. Launch MobileTrans > Backup & Restore to back up WhatsApp separately first; during the transfer process, try not to operate your Android device.