Extruder not heating to slicer temp once print starts

Your START_PRINT is wrong. The version that is commented out looks much better.
In addition, make sure to correctly pass the variables from the machine or filament gcode of the slicer. See Using START_PRINT and END_PRINT Macros for more details.

You can easily verify your slicer settings by opening a sliced gcode file in an editor.
Search for START_PRINT and it needs to look similar to:

START_PRINT BED_TEMP=60 EXTRUDER_TEMP=220