Was testing around some more and found that the active pathfinding is the setting causing issues.
When the character picks up a resource, the static mesh of the resource actor changes and the navmesh automatically updates. After those changes, the character is not able to move to the resource anymore.
This behavior changes if I move the resource far away from other objects even though the navmesh already marks the area between those objects green. Even if there is navigation all around the resource, the second movement does not work if it is too near to other objects.
Example with the navigation before first resource takeaway and after it:
