I have a Custom HTML tag in Google Webmaster tools that is actually very simple. It consists of the following code (a GTM Macro):
This tag is only fired on the Thank-you page on my website. This firing rule works fine, as I'm using it for a couple of other tags.
<img src="url1/?query1" width="1" height="1" /><img src="url2/?query2" width="1" height="1" />
Why is the HTML not executed? I don't believe it is a caching issue as the query parameters always have a different outcome. I believe it is a timing issue.
Update: I think I found a solution, but still it is unclear to me why it did not work in the first place.
This solution requires you to check the box: Support document.write