git diff shows differences but git merge don't see them

Hello.

diff show difference, which are really exists.

But merge refuses to merge them.

How this could be?

common (develop)
$ git status
On branch develop
Your branch is up-to-date with 'origin/develop'.
nothing to commit, working tree clean

common (develop)
$ git diff develop release/333-test --name-status
D 01_alter_koz_mapping.sql
D 02_fix_remarks_on_dict.sql
D 010_upd_subsystem_ent_docs.sql
D 00_create_user_fb.sql
D 01_insurer_payments.sql
D logs/20190531-115323.log

common (develop)
$ git merge release/333-test --no-commit
Already up-to-date.

It’s hard to say without having a sample repository to work with. But if I had to guess, it’s because the git diff form you used did a straight across diff between the state of the repo at develop and the state of the repo at release/333-test, but the git merge you did performed a three-way merge between develop, release/333-test, and their common ancestor. The three-way merge is smarter in what it can detect and generally ends up at the right answer more often than a simple two-way diff/merge.

I hope that helps!