FWIW: I appear to have the same problem: the inbox does not sync. All other sync (2 separate databases, stored locally, synced via Dropbox) works perfectly fine, but not the Inbox, on any of my devices. I have now emptied the inboxes (as they are currently like if “stand-alone”) and have created a single simple easily identifiable .txt file in each of the inboxes, and they simply refuse to show up on any other device. At the same time, if I add any file/folder/bookmark/whatever to the actual databases, they sync fine.
I have an iMac (latest OS, currently BigSur 11.0.1 & latest version of DT3, 3.6.1 the info box tells me).
I also have an iPad and 2 separate iPhones (X & 11, one private, one for work) all running the latest iOS version and the latest DTTG app.
That means I currently have 2 well synced databases but 4 separate inboxes. I get no error messages whatsoever from Dropbox or in the software/apps regarding the Inbox sync. Have been searching the forum and found this thread which seems to describe my exact problem.
It would be much easier to help debug sync problems if the devs would create a debug option which caused the apps to be far more verbose into the logs about what exactly they are doing at each step.
IMHO the biggest problem your users (especially beta testers) have is the lack of transparency. In despair we create little test files to try and be sure sync has worked.
A definitive unambiguous sync state number (like git uses) would be very useful so we can be sure sync has succeeded without digging around and creating arbitrary files just to try and discover what worked and what didn’t.
We all want these various edge cases to be solved but its very difficult to help if we are kept in the dark. Like mushrooms.
In DEVONthink To Go’s ? > Help > Appendix > URL Commands > Changing Settings, there is a SyncDebugLog option to enable.
In DEVONthink’s Help > Documentation > Appendix > Hidden Preferences, there is a SyncDebugLog option to enable.
However…
The information is accessible in the Sync.log when starting a support ticket in DEVONthink or DEVONthink To Go. For DEVONthink it can be found in the ~/Library/Application Support/DEVONthink 3/Cloudy directory, but we generally don’t advocate messing about in there.
This option is not enabled by default, nor should it be left on in the general course of things, as the log files can grow very quickly.
Also, if this has been enabled then disabled later, the log file will still be large. Perhaps @cgrunenberg has a thought on whether this could (or should) be pruned for DEVONthink. (I don’t know what access is available for this kind of thing in iOS.)
This should be only used temporarily, not always. In many cases this doesn’t help unfortunately as the issue isn’t a local one but caused by e.g. server or cloud issues.
Kind of difficult to open a support ticket ‘as mentioned above’ when the app (latest v3 Beta) crashes upon startup (and what appears the be initial sync routine). Have sent various TestFlight …never mind…TestFlight notification just arrived that new version update…sync (PDF issue) resolved, so far!