I'm a bit new to GitHub. Sorry in advance if this is a noob question.
I have 2 branches,
$ git checkout master
$ git pull origin master
$ git merge dev
$ git commit -m "Dev merged in Master"
I do not have enough reputation to add a comment, so apologies for writing this as an answer.
as @Jérémy Giuseppi mentions, you must always add files after any modifications if you wish to include them in your commit. When you resolved the conflict, you made modifications to files B but use of
git commit -m 'message' did not include those updates.
To avoid this in the future, I suggest using
git commit -a -m 'message', where the
-a flag tells git to add all modified files since last commit to the new commit message.
Checkout How to resolve merge conflicts in Git? to see a workflow of resolving conflicts in git