next_post_link doesnt work

Hello,
I have following code inside my loop-single:
<?php previous_post_link('? %link', '%title', true); ?><?php next_post_link('%link ?', '%title', true); ?>
And strange things happen! ??

It worked like an hour ago, I got navigation through my posts within the same category. However, due to the publication date edition, and plugin that allow drag&drop it showed some strange things.

So I’ve deleted posts (since I have 3) and posted them again. In same category, with same options as before.

I have nice previous post links, but the next post link doesn’t show!
What’s wrong?

btw. It works, when I delete the “true” from arguments. But that’s not the point. ??