1.7 is still in alpha phase so you should only use it if you want to live on the edge and report bugs. I asked because 1.7 has a feature to hide levels of the file manager, but that's not what's going on with you.
Did you change themes? Some theme's aren't wide enough to display all levels. Try the default theme to make sure the problem isn't the theme.
That's the only thing I can think of for only the top two levels showing and the third being hidden.
I don't think it's possible to downgrade. I did a test and the site broke. That's why you always make a backup of your entire site before upgrades or major changes. Or do all testing in a local install.
If 1.7a4 is working for you then I wouldn't worry about things. My sites are running with it. The bugs in alpha 4 aren't that serious and a new revision should be out very soon. most likely Beta and I expect it will be very stable for a beta. Nonetheless, in the future make regular backups of your site when it's working correctly ;)
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