I have analysed your case. I found a bug in WaveLab, but also an immediate solution for you.
First you need to understand the underlying issue.
In this dialog (this is a WaveLab 9.5 style, but you will recognize it anyway)
2017-12-17_13-01-40.png
you can see:
“Collection <-> IPRD”
But what you cannot see, is
“Album <-> IPRD”
This last item is something you have entered in the past, but which is not visible in the dialog, because there is currently no user variable called “Album”.
When the batch processing happens, WaveLab finds two entries for IPRD, and unfortunately, it might retain the one you don’t use (“Album” here, instead of “Collection”).
In that case, the proper metadata connection is not found and you don’t get the result you expect, with some missing fields.
I will fix this on the WaveLab side for 9.5.20 (for WaveLab to ignore the user variables that are not active).
But you have a solution today, which is to redo (from nothing), the XML Audio Description. In that way, some old user variable won’t “pollute” it and the batch process should work as you expect.
Tell me is that works for you.