I recently had to transfer an unreal project to a different device, now a bunch of objects are missing and I don't know how to get some of them back.

Its ok I figured it out.
Because I was using Booleans and stuff, all the data for the models were being stored in the _GENERATED folder which never downloaded when I was transferring the level data across.
I restarted the entire thing and when looking through the files to try and solve the issue, I found the folder and in it had all the boolean and model data that was missing before restarting everything, so in the end I just never downloaded everything correctly.