Wild Tremors
The hunting party eventually crossed over into prairie terrain. The terrain became a little harder to navigate, and if the Vandals made use of wheeled or tracked vehicles, then they would have slowed down to a crawl.
Fortunately, the legged transports which derived some of their shape from insects possessed enough maneuverability to walk over most irregularities in the terrain. They didn't even slow down that much when they had to climb uphill.
To speed up their progress, every mech and transport maintained their own antigrav fields. Though costly in terms of energy, sustaining it for a day or two wouldn't break their energy budget.
Still, if they kept the antigrav modules running at all times, then eventually they would run out of energy after a month or two. That was way too fast and would put them at a huge disadvantage.