PS My usual approach to fixing git-svn problems is to make a fresh pull of the repository. Time consuming, but you can do it in parallel with trying to fix the problem. Have a little race between you and git. Of course, this only works if you didn't have unpushed commits.
Open Git Extension and choose repository (if more than one)
Choose "Settings" from top menu then "Git Maintenance" and then click on "Delete Index Lock"
Git Extensions: Settings->Git Maintenance->Delete Index Lock
I was facing the issue, and I couldn’t even able to find the index.lock.
My environment was a little bit different, a cluster with multiple nodes.
The issue was encountered in the master node, and I solve it just by jumping to the worker node since the master node is chaired by all connected user