Why do files smear across to other branches when they have nothing to do with that branch

Hi I’m having an issue with the Gitlab which I’m running on cloud server. when I create separate branches to implement new systems and don’t merge that branch to the development branch and change branches I have files that pop up from the newly created branch on an old one. the files have nothing to do with the other branch. I usually just discard them on the old branch but want to try and figure out the cause because nobody else in the team is experiencing this?

Any guidance would be greatly appreciated