On some computers it can happen that scanning is not smooth, there a jumps in the scanning process, or the movement on the screen has a lag or delay.
Some computers have a combined Bluetooth and WiFi antenna and if the WiFi is active the Bluetooth transmission is interrupted frequently.
Since PocketScan needs to send big image data over Bluetooth this can cause the scan process to be abnormal.
As a work-around you can try to disable your WiFi connection while scanning in the Windows settings.
After you have done so, the scanning should be much smoother.