I am experiencing the same issue. I did not notice it initially and only realized it as I was reading through Wappler posts while drinking my pumpkin spice coffee.
I manually removed the standard html tags (html, head, body) from the existing content page and added the Wappler include and ac:route from another page that used a layout and modified it to make it work with the existing content page.
That’s a 5 years old topic, with an issue reported with a very old Wappler version.
If you have any issues withe the latest Wappler version please create a new topic and explain everything in details.