I have the exact same problem, and I also had the All in one SEO pack, installed.
It was also the SEO pack I could see as the last thing on the post edit page, so I tried removing the All in one SEO pack, and the settings came back – but now it gets peculiar – only for a while!
2 days later, without the All in one SEO pack I couldn’t see the rest of the advanced settings again, so I gues it couln’t be the SEO pack.
Then I tried all my other plugins, one by one, and when toggeling the Vipers Vide Quicktag off, my advanced settings came back, when activating Vipers again, my settings dissapeared. I’ve tried that 5 time in a row – everytime the same reaction, so I thought I had found the problem, and deactivated the Vipers plugin.
Now, without Vipers, the problem is there AGAIN!
The Advanced settings are gone for some few post. Most often the ones that I’m editing at the time. Also the comments turns off automatic for that peticular post, and I can’t set it on again, because the settings are missing ??
Now I have deactivated 2 plugins, and after a while the problem comes again, so I’m not sure it’s any of the plugins. I really don’t have a clue, and I’m also ready for almost anything, just to make it dissapear.
I have changed back to WP standard theme, with no effect, so I guess it’s not my theme either. Or widgets.
My advanced settings always stops in the middle of Categories og just after Categories, so I guess it maybe could be something with categories.
Toggling a plugin always makes it work again, then I can manually turn on the comments again, and the post works like before the problem. But even with the deactivated plugin, deactivated for good, the problem returns again a few days later.
No one in the danish forum has the problem.
Best regards Peter, Copenhagen