Gitlab_500 error_Whoops, something went wrong_ Unable to take a backup

System information:
Ubuntu 18.04
current user ;git
gen version : 2.6.3p62
Bundler version :1.17.3
rake version:12.3.2
redis version:3.2.12
git version:2.22.0

Gitlab information:
Version 12.3.5
DB Adaptor:postgreSQL
DB version:10.9
Issue Description: we are not able to access the project location and we are getting 500 error on the same. We hosted the gitlab application in our own server instance.
We are not able to take the existing db backup with this comment (“gitlab-rake gitlab:backup:create")
Error :rake aborted!
Caused by:
GRPC::Internal: 13:HasLocalBranches: cmd wait: exit status 128

Please help us to rectify the same .