He would commonly submit his application to the store and get critical feedback and very helpful comments on why it wouldn't work, what wouldn't work and in one case an architectural issue that could have caused duplication.
As a consumer, I've never had any applications fail to use iCloud effectively, everything I use that actually leverages iCloud (and not dropbox or $proprietary_syncing_method) just works wonderfully and predictibly.
the authors actual gripe seems to be from the developer who has not submitted a fully working version of his program.
I would ask him what specifically makes him think that it's the device causing the issue.. maybe add a contact through the webUI and see if it syncs, or modify data with another application that uses iCloud.
>Obviously I’m using more apps than just MindNode.
which apps, have they been updated recently? iCloud API's have changed in iOS8
Diagnostics is super simple stuff, don't blame everything before at least looking into the issue.