If you transfer a project that references separate assemblies or designs, they are not automatically transferred. The references will still work, but the referenced data will be read-only. You will not be able to make changes to this data from the destination project unless you follow these steps.
In the Fusion web client, click the Fusion icon
in the upper left corner of the browser to show a list of projects in the source hub.
Transfer all referenced projects to the same destination hub where you transferred the first assembly.
At the top-right of the Fusion web client, click your profile icon and select the destination hub to switch to it.

Verify that all the projects have successfully transferred to the destination hub.
In Fusion, open the the project you initially transferred, make a small unimportant change to it (such as hiding and re-showing a component), and save it.
This refreshes all Uses and Used In data for the project. Until you do this, the transferred project will not show any information under Uses and Used In.

Repeat the previous step for any drawings referenced by the transferred project.
You should now be able to work in your transferred assembly as you normally would.