Sporadically I get this error when pulling from a private repo to 1 or more of my virtual machines (Fedora/Linux Mint/Centos 7). See below. Retrying the command a few seconds later makes things work !!

First try fails:

✔ ~/repos/emacs_init_el [master|✔]
22:48 $ git pull
error: cannot lock ref 'refs/remotes/origin/master': is at 95f898b8d0cd4724b37f074456127d0e62ead43c but expected c0b18ba12cde6130dcf005631c84b7a166661fb1
From bitbucket.org:pymaximus/emacs_init_el
! c0b18ba..95f898b master -> origin/master (unable to update local ref)

Second try a few seconds later is successful:

✘-1 ~/repos/emacs_init_el [master ↓·1|✔]
22:48 $ git pull
Updating c0b18ba..95f898b
Fast-forward
init.el | 3 +++
1 file changed, 3 insertions
✔ ~/repos/emacs_init_el [master|✔]
22:48 $