What is the purpose of these movable panels on the MiG-35?
The aerodynamic devices in question here were already present on MiG-29KUB which is a parent version of MiG-35: Wikipedia: MiG-35

The devices are in fact, as some have suggested, Krueger flaps, as Russian test pilot Pavel Vlasov describes in this article: The MiG-29KUB: in the Russian and Indian skies for 9 years


  "It is a modern multirole plane with revolutionary fighting capabilities, with an increased payload and a longer list of weapons," said Pavel Vlasov, Honoured Russian Test Pilot, Hero of the Russian Federation, and General Director of the Gromov Flight Research Institute (and Head of the Flying Service at MiG until 2010). He noted at the same time that the MiG-29KUB featured a range of new solutions, such as Krueger flaps, a new flap design, a modern fly-by wire control system, and significantly improved piloting conditions


In addition to calling them Krueger flaps, this article also gives the devices the acronym LEVCON, leading-edge vortex controllers: SlideShare: Fulcrum Reloaded (see page 4)

The purpose of Krueger flaps is to increase the coefficient of lift of the wing, and to improve slow speed handling: Wikipedia: Krueger flap

After facts some speculation: the reason the Krueger flaps are not deployed in some of the pictures with gear extended is probably bacause they are not used in take off configuration, and the pictures most likely have been taken in t/o situation, not while the aircraft is landing