Hey there @ninalv! Welcome to the community! So when you migrate a project to 5.1 it makes a copy of the entire project instead of just migrating (for safety reasons in case it fails). So you were working in that copy. Relaunch 5.1 and you should see the 5.1 version of your 5.0.3 project in the list. They aren’t linked at all. So you could migrate the 5.0.3 changes to the 5.1 project if you’d like, but the reverse is a bit harder.
Either way the gist is that I think you technically made changes in another project altogether!