Please note, this is not caused by the template. It is a Blogger system feature. We cannot control this via the template, sadly.
If you are using a template which features a grid layout then you might notice that the number of posts displayed changes randomly, even though you have changed it to a specific number.
If you have lots of images or long post content, Blogger automatically stops displaying posts on the homepage and other post listing pages.
How to fix it
Thankfully, there is a workaround to fix this. If you add a 'read more' button after the first image and paragraph of your posts, this will trick Blogger into showing more posts. You will need to add the 'read more' button to at least all of the posts shown on your homepage. You may need to add it to more than this before Blogger will display all posts correctly.
Please note, this is not something which is caused by the theme. It is part of the Blogger system itself. If you think that this is a bad feature, you should let them know on their announcement post. Hopefully they will change it!
Or you may wish to upgrade to WordPress, which allows you to have full control over your site content.
Article tags: home page, homepage, post, next, post number dont change, post number