Sometimes when you migrate assets, to much gets migrated, an option t uncheck assets for migration would could help, increase workflow.
When you migrate an asset all the assets that it references/uses are also set to migrate because they are required or used by that asset so they must also migrate with it for it to function. If you migrate multiple assets at different times that use the same assets the duplicates will present with a warning to override the existing copies in the project that you are migrating to. If you wanted to migrate a Material it will also grab all the textures that it is using to migrate with it, if it didn’t the migrated material wouldn’t open or work in the project that it was migrated to, that doesn’t seem like a very good time saver to me…more like asking for a bunch of headaches.
In our project we use child characters, so we got a master blueprint for our characters, with a custom component. If i now want to migrate one child blueprint, it fetches all the other child blueprints, which are not really required, and which makes migrating our assets a tedious task (hundreds of migrated assets in different folders, which are not required).
Also many of our characters share a master skeleton, on migrate, all the socketed preview meshes get migrated as well.
I think what is happening is that when you try to migrate the first child it is grabbing the master, which in turn is grabbing all of its children and then they in turn are grabbing all of their dependents and so on…Yeah I can see how that particular situation would become a tedious task.