Hi there,
Can I see the read more link you’ve added? Perhaps the link specified on the link you’ve manually created doesn’t point to the correct link.
Also, you seem to be making the Latest post manually but is it dynamic? If isn’t and you wish to make it always display the actual latest posts consider using a plugin.
If I may suggest, consider using WP Show Posts to show the Latest Posts on your sidebar rather than making your own custom block. It actually has its own Read more button built in so you’re sure the Read More button works.