Marlin is an optimized firmware for RepRap 3D printers based on the Arduino platform. Many commercial 3D printers come with Marlin installed. Check with your vendor if you need source code for your specific machine.
When G34 failed on the first probe attempt and home after G34 was not enabled, a default value of 100k was still loaded in z_measured_min causing the Z position to be overwritten with a drastically out of bounds correction. The prevents position adjustment on an error escape, adds additional debug statements, and resolves an iterative clamping error that would cause successive runs to fail probing.
When G34 failed on the first probe attempt and home after G34 was not enabled, a default value of 100k was still loaded in z_measured_min causing the Z position to be overwritten with a drastically out of bounds correction. The prevents position adjustment on an error escape, adds additional debug statements, and resolves an iterative clamping error that would cause successive runs to fail probing.