Problem with the Z on my Printrbot

My students are creating prints in Tinkercad and bringing them into Astroprint to slice for their projects. We are saving them as an auto0.g file on an SD card and loading it onto my Printrbot Metal Plus. THe issue comes when it begins to print as the Z dips lower than the settings and digs into the print bed. I have no issues printing directly from Cura or Pronterface and the Z is perfect. Can anybody help out?

Could you tell me what start GCODE do you have in your Cura Profile? I think it’s likely due to that. If we get the right one, we can update our profile in AstroPrint

G21 ;metric values
G90 ;absolute positioning
M82 ;set extruder to absolute mode
M106 ;start with the fan on
G28 X0 Y0 ;home X/Y
G28 Z0 ;home Z
G92 E0 ;zero the extruded length
G29 ;initiate auto bed leveling sequence

I have updated the start GCODE for that printer model. Could you have your students sync their profiles and try again?