I noticed that when going back to the thread the draft is from, doesn't always reconnect it.
When I open the draft with the right thread open, it works. But when I open the draft, recognize it, then navigate, it doesn't The draft stays open but won't be linked to the post. Or at least so it appears.
The screenshot below is after clicking in the textbox of the thread, hoping it would continue where I left off.

Copy-discard-paste works in this instance, but it is a bit clunky. I can also refresh the page then open the draft, then it works. And I just checked: it doesn't connect to an unrelated thread