The reason this happened is because of how the
Export.image process works. Paraphrasing the documentation provided by Earth Engine which states: "If no region is specified for export, the region defaults to the viewport at the time of invocation." Basically, you were only viewing part of the image when exporting and it cut off the bottom.
Generally, it is good practice to provide the
region parameters when exporting images to avoid this problem. Here is an your example that exports the full image (starting at line 128):
///////////EXPORT CLASSIFIED IMAGE//////////////
var exportRegion = studysite.geometry().bounds()
folder: 'GEE data',
Notice that the
exportRegion variable is extracted from the study area you provided and then passed as a parameter in the export task. Here is the full working link.