Git merge does not merge all files and changes but just a few.

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Hi, i have a git repository with 2 branches lets say branch_1 and branch_2.
when i use:
git checkout branch_1
git merge branch_2 branch_1

when i run above commands it merged the branch 1 and 2 but it does not merge all files but just a few.
i assume that the issue is because i had some files in branch_2 before which i deleted from branch_2 and later added the same code files in branch_1 to keep them in a separate one, may be this is why it is not allowing to merge all files of branch_1 into branch_2.
I want to merge all files from branch 1 and 2.
Any help will be appreciated.
Thanks in advance.

What I have tried:

git checkout branch_1
git merge branch_2 branch_1