Unexpected merge conflict

Summary

Merging branch A in to branch B generates a merge conflict when no changes hav been made to B

Steps to reproduce

What is the current bug behavior?

We use branches a lot in our team. We also have staging branch and a master branch. The master is in production. We only merge from staging into master. Nothing else goes into master. But recently we have started getting a merge conflict when we try to merge staging into master and it shows that staging is X commits behind master.

The last X commits on master are the ones that relate to the last time we merged from staging to master.

This has started only after GitLab upgraded their systems about a month ago.

What is the expected correct behavior?

Our merge from staging to master should never have conflicts since we never directly change master. The only thing that happens on master is that we merge staging into master

Relevant logs and/or screenshots

Request to merge staging into master The source branch is 2 commits behind the target branch

04 Jul, 2019 2 commits

Merge branch 'staging' into 'master' 2 weeks ago

Promote from Staging to Production 2 weeks ago

Possible fixes

Merge Master back into Staging, resolve conflicts, then push from staging to master