I believe this is more Dropbox issue but I posted it here since someone might have a solution.
While describing the issue, the sync problem got fixed. Below are my steps:
My iOS devices stopped syncing via Dropbox today, with message "Failed to list remote data folder in Dropbox".
After I stopped syncing and started sync again via Dropbox, I get "Error Listing Keychains"
This happened on 3 iOS devices (iPhone and iPad) across 2 different AppleIDs.
I can still synch 1PW on Mac computers.
When logged in to Dropbox on Mac I can see all folders, subfolders and files.
However, on iOS devices logged in the Dropbox via the iOS app I can only see top level folders and files under them. If there is a subfolder in Dropbox, I get "Unable to Load Folder". This is true for any folder with subfolders on Dropbox, not only 1Password.
In addition, logging to Dropbox on iOS via the web 1PW browser, I can see all folders, subfolders and files, same as on the Mac.
I have deleted Dropbox app and re-downloaded it again on the iPad. I got a message in 1PW "Failed to download file from Dropbox". The message went away after I clicked Sync now.
The file name that failed started with B7BD9......... . This file does not exist in 1Dropbox.agilekeychain ... Data folder.
So all is working, I re-downloaded Dropbox app only on one iOS device (iPad), but Dropbox sync now works on all devices, both AppleIDs.
1Password Version: 5.5 and 5.3.2
Extension Version: 4.4.3
OS Version: 10.10.5
Sync Type: Dropbox