At which point in the sage in the above post did you query the rest api?
I’ve queried it at the end of my described steps. This was when the sync made no progress and was before I removed GarminExpress.exe manually from device C to get in sync again (automatically).
Somehow, I’ve had two fresh setups on different hardware/networks the same day and they failed. My feeling tells me, we’ll find the culprit better when debugging the two device cluster at Fresh setup with 2 devices, sync stuck with no progress - #8 by Catfriend1 .
This setup used: NTFS (A) - ext4 (B,D) - zfs (C) as file systems. The referenced other topic used ext4 - zfs fs.
[[ May zfs have to do something with it? I’ve freshly setup both servers (independent from each other) and the zfs ran fine from the first moment. zpool status -v and zpool scrub showed no errors after checking both appliances. ]]