When exporting a VDB with a User Defined Function, the information about the UDF jar is not present in the resulting dynamic VDB file.
With regular VDB archives, the UDF jar is added to the lib/ directory within the archive and is referenced like so in META-INF/vdb.xml:
This approach is not possible in case of dynamic VDB defined only as an xml file. It is, however, possible to create a module on the server with UDF jar and then reference it in the *-vdb.xml like so:
It is currently possible to define such property manually in the VDB editor before exporting, but Designer should be able to define one automatically, or at least warn the user when there is a UDF jar present and the lib property is not defined.