If you save a post in Magento 2 Blog, your post is not saved and you are redirected to the Magento dashboard, most likely it happens when the post has a lot of related products or posts. This issue is connected with your server PHP configurations.
The max_input_vars PHP setting parameter defines the number of requests (posts) data PHP can receive. When a blog post has many related posts or products a lot of data goes with the request to PHP and it just doesn't receive part of this data.
In order to fix the issues with post saving:
1. Change the value of the max_input_vars parameter from 1000 to 5000 in the main php.ini file on your server.
2. Restart the Apache/Nginx or PHP-FPM if it is used.
Note: you need to have the superuser server permissions to be able to change this