The end of php ?> after your loop does not appear in your code…
Hello, sorry to not answer to your question directly, but I proposed a different approach.
why not use an another category “slider” per example. With it, you just need to filter in the loop this category ? In the table of posts, the authors will see which post are tagged “slider” or not (In your Figure2 it is not possible actually). I thinking it will be more ergonomic for them.
Hi
Is Flexible Content Field plugin actived ?