I’ve never known this happen (touch wood).
If it is fusion or vectric caused you would see the nose dive in the gcode created.
If it happens when flattening the boards it may be related to the cables and connections being strained and opened, causing disconnects (if like me you may not use the fully extent of the 1F unless flattening the wasteboard, if that is the flattening you refer to). If you search the forums there are posts on loose connections and symptoms.
For example:
Z axis is crazy (solved, replaced extension wire) - #4 by Aiph5u?