Hi,
Im using three MAC’s (OS X 10.11.12) with DEVONthink 2.8.8 each (one on trial).
On my webdav server (SuSe with Apache Server (Version 2.2.4)) I have created a relating structure on which my DEVONthing should sync.
I know that the webdav works since I’m using it for quite a while now with iPad’s Mac’s PC’s etc.
From outside I’m using port 81 (i.e. www.mynoip.org:81/mywebdav)
But DEVONthink does not work. It starts to sync, states that 11 out of 12 objects are done, waits for a while until the protocol window shows an erreor that the system could not connect to the specified host.
What am I doing wrong?
New behavoir:
I now mounted the webdav drive externally on one of my MAC’s and added an ‘existing local sync store’ to the installed DEVONthink.
First sync attempt: No problems 
Sync completed.
Next sync attempt: Protocol window states that the database metadata could not be opened because it does not exist!?!
I granted 0777 to the webdav user on my server because I slowly get mad. No luck 
Does somebody have an idea?
Could the redirected port 81 eventually cause the problem? But then: Why only with this software while all the other tools I’m using are working?!?
Sadly you are not alone, I have been fighting with this problem for a long time with no success.
Some users report that it is working for them, so technically it must be possible but so far no rhyme or reason. Sadly Devonthink is the only program showing this behaviour, other software uses the Webdav protocol with no problem whatsoever.
I am still in touch with support and should a pattern emerge, I will of course post here.