Problem: admin-ajax.php 404() for both back and frontend
in the frontend: the pagination using ajax is not working
error: POST hidden link 404 ()
at the backend: everytime we tried to save or edit settings it has an error message "Not saved" but when we refresh the page the changes has been saved, its wierd and also we cant add any post type or views
That will create a file debug.log in your /wp-content/ directory which you can examine in any text editor.
Try visiting the Toolset settings page or making some updates to the View again and then inspect the log. If you don't find the debug.log file it means it didn't generate any warnings or errors.
Then, try switching theme to twentyseventeen and test again.
Finally, de-activate your non-Toolset plugins and test again, and let me know what you find. If that resolves the problem it should be possible to identify the source of any conflicts by a process of elimination.