Doh, I forgot all about that…. My brain has been melted by working out multiple product schema per page.
The blog breadcrumb is now working beautifully. I did as you suggest and made an additional new hook for the Blog main page, and changed the hook location to be “inside_container” on that one instead of “before_main_content” and it works like the bomb. Thank you so much. My thinning, grey hair lives to fight another day!