If any of the above messages is displayed on the LED display then it means there is a problem with the Z limit switch. it is either that your Z limit switch was not getting pressed properly or something is preventing lever of the switch from switching.
Z-switch broken (UM2)
This gets displayed during the ‘homing’ of the Z-axis, Z limit switch isn't pressed
1. Check if there’s nothing lying underneath the platform. If so, remove that first.
2. When it’s still giving problems, bend the lever of the limit switch slightly.
Z-switch stuck (UM2)
This gets displayed when something gets stuck in the Z limit switch due to which the lever doesn’t switch back and remains pressed. You will also see this by the fact that the Z-axis raises upwards without lowering first.
1. Check if anything is blocking/pressing the Z limit switch; if so, remove it.