Some possible reasons for sync to fail are outlined below for you to check:
Sometimes people forget Leaf batteries are 2s and put 7 leaf batteries in as 7s instead of 14s). Device Sync tests the communications for the cell settings and tells them their place in the pack and what limits to operate at.
This would mean no responses come back, hence the failure.
WiFi is read-only hence you need to change to USB mode.
The status icon is:
instead of:
Distributed cellmons are powered by the battery they are attached to and need a minimum of 2V power.
Depending on changes made, this can affect communication sometimes.
Device sync is only needed in decentralised systems. This will probably still mean that the wiring does not match what you configured but the consequences are less dire.