git checkout develop, then git checkout startingBranch caused me to not find dependencies

So I am able to run my app successfully without hitch while on branchOne I wanted to work on another fix so I wanted to switch to develop branch and then create a new branch off of develop.

I did git checkout develop, tried to run the app, then I got a warning that my project was not in sync with my podfile.lock so it couldn't run the app. Then I did git checkout firstBranch to switch back to branchOne but when I try to run the app this time it fails because it cannot find dependencies.

Why is this happening?