Migrate asset results in unrecognizable data

Hi there,

I was given a project A which I needed to extend. Now I want to migrate some of the assets to another project B. However, when I open the other project B, some of the assets don’t show up in the content folder and yield the following error:

LogLinker: Warning: The file '<path-to-uasset>' contains unrecognizable data, check that it is of the expected type.

My first guess was, that the exported assets depend on some plugins in the source project A. Then, I only migrated a texture. Same behaviour.

My second guess was, that this might be caused by the missing asset source files (e.g. the actual texture image). So I exported the texture somewhere onto my harddrive, which worked fine. Then I changed the source file of the texture asset to the newly exported texture image and migrated again.
This time the texture showed up in the new project B.
I also tried this with a mesh. Same thing. Didn’t work with the source path to the non-existing asset but worked with the source path set to the exported mesh.

This suggests that the asset source files need to be available when migrating assets to other projects althoug all the required information seems to be present in the uassets.
My question is, is this correct? I couldn’t find this requirement in the documentation.

The followup question would be:
Is there a way to bulk export all the assets which have source files into a folder and replace the source files with these newly exported files?

All of this is done with the same engine version 4.19.2-4033788+++UE4+Release-4.19.