Hi Connexinet,
Thanks for your reply.
I have disabled all my browser extensions as well as disabling all my Wordpress plugins, switching themes and trying a variety or browsers, all which generate the errors.
I am using a large image card with summary (through Yoast, though I have tried without) and even though the twitter validator displays the link correctly, when actually using it, the images do not work.
I have tried various troubleshooting recommendations with no result - leaving me to assume it is caused as a result of these errors.
I looked in my header.php file to see if I was using and semi-colons incorrectly, but I’m not. I know very little about this area but it would seem the error comes directly from Twitters own script?