The Mode button on your Wireless Gamepad F710 swaps the functionality of the directional pad (D-pad) with the left thumbstick. When the Mode button is lit, the functionality is being swapped.
If either your D-pad or thumbstick isn't operating as expected, press the Mode button. This should resolve a situation where the D-pad is acting like a thumbstick or vice versa.
Please see Knowledge Base article 21368 for instructions on contacting Logitech Technical Support.