Post titles not displaying since switching to Latest Post Block

I’ve sorted the problem below but can’t see how to delete the post

Hello, I set up a static home page using the Latest Posts Block in the Wordpress Gutenberg Editor. This pulled the posts through but the post titles have been changed to a URL

Most but not all of the posts were created using the Classic Editor and they all now display a URL instead of a title.

I went into the Block editor and added a title block to the post in the image below - the title shows as a heading but the URL link placeholder still appears

Can anyone explain where the URL form of the title has come from please, and how to get rid of it, preferably without going into the HTML as I’m not familiar with code.

Thanks
Sue Watling