DIAGNOSIS The mower's grip is insufficient for the terrain. The factory-installed slick wheels lose traction on slopes, especially when damp.
FIX Install spiked wheel kits (official Husqvarna accessory). These replace the standard wheels and provide significantly better grip on inclines and soft ground.
IF THAT DIDN'T WORK If it still struggles after installing spiked wheels, your slope may exceed the 430XH's rated 40% (22-degree) maximum. You may need to grade the area or install a perimeter wire 'lift' to guide it through the dip.
HEADS UP Spiked wheels are more aggressive on the lawn. On flat, firm turf, they can cause slight scuffing. Install them only if traction is a verified problem.