It sounds like there might be an issue with the hydraulic steering system. I'd suggest checking the hydraulic fluid levels and inspecting for any leaks or blockages.
Another possibility could be a worn-out power steering pump. If it's not providing enough pressure, the steering can become erratic.
Make sure to also inspect the steering gearbox for any signs of damage or wear. This can also contribute to steering issues.
If all else fails, you might want to consult the vehicle's manual or contact the manufacturer for specific troubleshooting steps.