I am happily using Syncthing between 2 computers at home (6TB, 1.3mio files). 13 folders, some send & receive, some send only, some receive only based on where source of data is. Second device is somewhat backup to master data on first device and vice versa. Everything workgs great!
With untrusted devices functionality I added third untrusted device off site, somewhere far away as “offsite receive only encrypted storage” in case of losing my two primary computers. For just part of files (3TiB)… This third device has very limited speed connection (like 1MiB/sec) so I am counting on very long times to transfer data there. Which is no problem, I can wait for it. Unfortunately, every restart of that third device is causing transfering 6GiB of index data! No delta-indexes used! … Is that normal behaviour? … I tried -reset-deltas on all machines, still there are messages on third device claiming both home computers “is delta index compatible, but seems out of sync with reality” … Why is that?! … And what can I do to make it work? Sending 6GiB each time on that slow line is propably too long to actualy sync something (which is not, because no files changed at home computers for most of the time)
Is there problem have untrusted device linked with two trusted, which are linked too?
Looks like new added folder and shared on all devices have no this behaviour (is not listed as out of reality index). Are previous folder somewhat not migrated/prepared for this function?
 - oh, sending again and again this amount of data is each time I pause/unpause folders on the any home computer … can’t be right