Wasn't sure how else to respond to you but I put this thread on cyclical and unstickied it. It shot to the bottom of the catalog so I put it back on sticky. I deleted about 500 posts, they were all from 2016, unsticked it again and it still shot to the bottom.

If you're logged in and hit the moderate thread button below the captcha you should be able to mess with the sticky, cyclical and lock options. You don't need to go to moderate thread to delete posts.