This sure is another learning point. The 32hrs print had to be cancelled at the 18hr mark. Nothing like agonizing over having to stop a job half-way through it's progress.
So it seems that very tall, 'stand-alone' supports are wobbly. So when the print head moved across them, they don't hold their shape and thus start to not print properly/just kinda spew filament wherever.
The red square represents roughly where the support was before. So I added more and now we should be good. I also had to do the same at the tail as I noted it was wobbly there too.
You are always learning here, no doubt about it.