I've purchased a set up 1Password 4 for myself and three family members in the last week. Using DropBox sync has been problematic for two out of four of these setups.
On my iPad and iPhone 5 DropBox sync proceeds very slowly and often ends with an alert symbol over the DropBox icon. Usually tapping on this reveals nothing but at other times it reports the error message:
The operation couldn't be completed (NSURLErrorDomain error -1001.)
Sometimes the error message on the iPad is:
Failed to list data folder in Dropbox
The operation couldn't be completed. (dropbox.com error 404.)
Meanwhile iCloud sync proceeds quickly and, apparently, repeatedly. I'm not sure how valuable iCloud sync is in this instance since I assume it's not connected with 1Password 3.9.6 on my Mac which makes no reference to iCloud.
I've tried switching DropBox off and on again (initiating the usual DropBox approval screen each time) on both devices with no useful result. I've also rebuilt the data file on my Mac for good measure.
What should I try next?