I know that Indexing is not supported in DTTG. But does that mean, once indexed folders are added to the database on the Mac, DTTG can’t synchronized anymore via bonjour? I thought that indexed folders would simply be skipped in DTTG.
For the first time I use indexed folders on the Mac and synchronizing now freezes on DTTG and after a while stops with a broken connection error massage.
DTTG can’t synchronized anymore via bonjour?
No, that is not correct.
I thought that indexed folders would simply be skipped in DTTG.
That is also incorrect.
While indexing directly in DEVONthink To Go is not possible, you certainly can use indexing for databases synced between a Mac and iOS. The indexed files are just imported into DEVONthink To Go as they can’t be linked outside the database in iOS.
The error you’re reporting would have nothing to do with indexing files and more likely to be a network issue or the machine acting as the Bonjour server going to sleep.
In DEVONthink To Go, select ? > Contact Us to start a support ticket. Thanks!
Thanks for your reply, and sorry for my incompetent guessing. The synchronizing was working fine before and didn‘t work anymore from the moment on the first indexed folder was added to my database.
I will do as you suggest and start a support ticket.
No worries and no incompetence detected 
The sync issue is almost certainly coincidental.