remote: Counting objects: 3442754, done. remote: Compressing objects: 100% (515633/515633), done. remote: Total 3442754 (delta 2898137), reused 3442437
I have seen this issue when the machine from which the "repo sync" or "git pull" was done had very low memory. I have seen this multiple times and checking the memory it always had 0GB free memory. This also happened when the user machine's OS was upgraded to Ubuntu 14.04 and had the same issue of memory being insufficient though memory was managed well with a previous OS version.
Running the same command from a more powerful machine worked or trying this from a different OS worked.
This is not an answer but i had seen this issue, so an observation and workaround if the issue is related to memory.