I have recently updated my git (2.7.4.windows.1). Since then pulling from github produces output like this:
$ git pull --rebase
Fatal: TaskCanceledException enco
There appears to be some relation between the setting of proxy options inside your global .gitconfig file and the need to clear your credential helper setting from the system level. I recently removed git http-proxy and https-proxy settings from my file for security reasons, and began receiving this message, then a pause, then a prompt to log into my external git repository. This happened with every fetch, push or pull. I didn't want to replace the proxy settings in my .gitconfig, so here are the steps that worked for me:
git config --list --system
git config --list --global
These will give you listings of all your system and global level settings. This confirmed that it was set to credential.helper=manager in the system namespace, and credential.helper=wincred in the global namespace. To remove the interference on the system level:
git config --system --unset credential.helper
All git command reverted to normal, with no error messages or delays.