I had this issue too, but was able to resolve!
On the Home screen where all of your projects are listed, you might notice that the left navigation pane separates projects saved to your iPad vs. projects saved to Dropbox. DropBox syncing seems to only work for project saved to Dropbox!
To resolve this, click Edit on the top of the pane, and then drag your project from On iPad up to Dropbox.
I had the same problem. I found it was the name I was using for the project on my PC was too complex. Once I removed all the extra (example HQ.v1.3) to (HQ) everything worked fine.
For future reference, replacing the periods with underscores probably would have worked as well. Periods are meaningful in most operating systems, so it’s not unusual for them to cause strange behavior when used in filenames.
Katherine
I am having the exact problems mentioned in this conversation, except I am trying to synch between my iPad and my macbook.
Soooo distressing as I am travelling overseas in two days and I badly need to take my project but can’t take my laptop as it’s too heavy.
WHy? Why Why?
I even bought and paid for the iPad version of Scrivener especially for this journey. Drop box is sitting on both my devices and I can see the folders in both and I have followed all the instructions but it won’t load.
Why?
Because something in what you have done did not follow the instructions.
The most common error is that iOS Scrivener hasn’t been setup to actually look in the correct Dropbox folder.
Where are your Scrivener projects located on the Mac and how is iOS Scrivener linked to Dropbox?
Okay. I found the problem! 
My original scrivener (which I bought many years ago) hadn’t been updated. I did all the updates and followed the instructions in this link, and it works.
I highly recommend the following link:
agdaws.com/2016/08/how-to-se … scrivener/
YAY!!!
(and yes, i think there was a file location problem too)
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