https://www.hse.gov.uk/safetybulletins/scissorlifts.htm

The JLG 500RTS scissor lift is equipped with an oscillating axle which allows the machine to be driven on uneven ground with the platform in the transport position. JLG 400RTS models have a similar design of oscillating axle lockout valve (and lift/drive limit switch). As soon as the platform is raised out of the transport position (by the scissor arms being raised off the chassis), the oscillating axle should lock preventing further rotation of the oscillating axle. This functions by a plunger valve (the oscillating axle lockout valve) mounted on the chassis being released under spring pressure, preventing further rotation of the oscillating axle. The position of the oscillating axle lock out valve is shown in figure 1.

Also:

https://www.cranetech.com/blog/ees-axle-lock/

Equipment Explained: Oscillating Axle Lock System

The stability of the machine when moving around on uneven/rough terrain can be a challenge. That is why many aerial lifts are equipped with an oscillating axle lock system. This safeguard ensures stability when the boom is rotated over the side and ensures the lift maintains capacity. Unfortunately this simple feature may not be known or is overlooked by operators and maintenance staff.