Thanks for the video, Anh.
I created a fresh install of WP just for this, installed Meta Box, MB Custom Post Type, MB Relationships, and the Twenty Seventeen theme, and duplicated the steps you took in your first video. And yes, it’s working for me right now — order is preserved after updating a speaker post.
But our staging and production servers are still bumping the last updated post to the bottom of the list. I’m going to slowly add back in pieces of our staging environment (plugins, theme files) to see if I can pinpoint what it is that causes the posts to reorder. If I find what it is, I’ll report back here.