Windell, thank you for your idea to copy it into a new document. I isolated it down to 1 shape on 2 documents, the original (which exhibits the bug) and the new document (which does not), I went through every attributes until I found the culprit.
It turns out that the
svg element needs to have a height and width defined.
How it interacts with the hatching working bizarrely at different angles is beyond me :).
Thank you again for the super nice hatching algorithm and your help here. I hope this finding ends up helping someone else.