New pages do not allow any new content

I have a WordPress system (5.5.1) and I am using the plugin Lazy Blocks (2.1.1) to create custom blocks.

I have reached a point that something weird happens. When I create a new page, the interface presented allows me to set the title, but it is not possible to click anywhere to add blocks.

If I switch to the code editor for the page I see that the page was prefilled with this code:

I have tried deleting this code, and return to the visual editor, but I am still unable to add blocks to the page.

What is happening? How come my page is pre-populated with this element, and why can’t I add any blocks to the page?

UPDATE
Notice this only happens for pages. Not for posts.