I have a Rich Text custom field in the PO that I'd like to print on the PO. I'm getting an expected error. The field contains HTML tags such as span, style and break. Is that because of it?

Rich Text fields don't play nicely with Advanced PDFs. Years ago I came across the issue that it would randomly remove the forward slash from self-closing tags (e.g. <img />) making them invalid XML. From chat here I've seen additional issues come up

I had the same with HTML code on a custom field in the Subsidiary. It does work. But I would review the code on the field first and if it doesn't work try to move most of the span and style stuff to the Template instead.