Could you please confirm if you are facing an issue using the Highlight Text option in the Annotations menu or you are facing an issue in highlighting the tex to copy it ?
Also if it is related to annotations menu, please refer to the link below:
Let me know if the issue still persists.
Seems to be a device specific issue. Have you tested this issue on other Android devices and also with other PDF files?
Please calibrate "G-Sensor" or other touchscreen sensitivity option on your device and then try to replicate the issue, options should be under your Device Settings -> Device/Gesture.