Hi Diana,
As a possible solution, I would first recommend re-saving your permalinks under Settings > Permalinks.
Other potential causes of this issue are:
1. The page name is the same as an category/taxonomy name
2. A plugin
3. Improper editing of a page template (This might be the case. Based on the markup, it looks like a template part has been added to the blank canvas page template.)
If the issue is number 3, you will likely need to reset/restore the page template to its original state within the Editor.
Thanks!