There is an issue with PHP zip in regards to 2GB. Search of Tracker shows the issue is across the board ... Mac/Windows/Linux. The makers of PHP are the only ones who can really fix ... no change in Moodle code will matter.
To the best of my knowledge there are only two approaches for large courses:
1) in the course, delete large resources - uploaded videos/audios if any (make sure you have those individual files archived or have access to them for later re-linking/uploading). Purpose: get the backup below the 2Gig limit.
2) Warning ... it involves 'manual labor' and command line. First a question: after failure, does the dca63bd27d4555d5af611f6c1e8f10af folder still exist in temp/backup/
If so, have you inspected its contents?
'spirit of sharing', Ken