Why would a merge from one branch into an existing branch not apply new changes?

Summary:

Merging branch feature/performance-management into feature/combined-perf-hr-branches is not bringing in the code changes from feature/performance-management. Why?

Content:

We are managing three branches for our development work:

1. feature/core-hr – Contains changes for Core HR pages. This branch will be deployed to production first.
2. feature/performance-management – Contains changes for Performance Management pages. This branch will be deployed to production after the feature/core-hr branch.
3. feature/combined-perf-hr-branches – A combined branch used for testing, containing the merged changes from both feature/core-hr and feature/performance-management.

Since feature/core-hr and feature/performance-management will be deployed on different schedules, we keep their changes isolated. However, to allow testing of the full feature set in a shared environment, we regularly merge both branches into feature/combined-perf-hr-branches and deploy that combined branch to our test environment. This approach has worked well so far.