Can you create a 30 second clip of one of these failing files to send me for testing?
Perhaps a tool like Audacity? depends on format.
re: Album as Series - That is exactly the tag field I use to set the series.
re: metadata coming from file name - the plugin does that as the last ditch effort to get something when it can't get the metadata from the tags. I do my best to recognize the most common file naming conventions, but I might get the pattern wrong.
The real question is: Why isn't it getting the tags? And to learn that I need to dissect a file that the plugin fails on. Preferably a small file. ;-)