error when pushing branch into github - 'remote: error: cannot lock ref 'refs/heads/master': Unable to create'

I get the below exception when I try to push my local branch into master.

#!text

Total 0 (delta 0), reused 0 (delta 0)
remote: error: cannot lock ref 'refs/heads/master': Unable to create '/data/c01/n08/p/vp0664/data/d-41/r-27032041/refs/heads/master.lock': File exists.
remote: 
remote: If no other git process is currently running, this probably means a
remote: git process crashed in this repository earlier. Make sure no other git
remote: process is running and remove the file manually to continue.

• I get this exception only when pushing the master branch.
• I get this exception when pushing the master branch even from other computers.
• I get this exception even when I try to merge dev branch into master on bitbucket website directly not involving the local computer.

Because of the above 3 reasons I don't think it is a issue with my local .git folder. I can't think of what the possible cause is.

I have tried solutions available in answers to similar exceptions, but all of them are about cleaning/purging/manipulating the files in the .git folder but I get this same issue even from different computers and even on the bitbucket portal itself.

The repository is a private repository - https://bitbucket.org/chorus_nz/cfi-documentation