I have had Syncthing (v1.29.3) stop working, on a single Windows 11 device, twice in five days. Each Folder appears with a status of “Unknown” and the other Devices show last connected as “never”.
The change that may have precipitated this is that the laptop in question is now kept running while shut, connected to a KVM switch. Previously it was left open, running, and I used its built-in keyboard and monitor. I haven’t changed anything else on this machine.
Syncthing’s log indicates that Windows suddenly stops Syncthing’s access to the network. The Windows Event Log shows that this happens right after the laptop comes out of “Modern Standby.”
I’ve disabled Modern Standby and am now waiting to see if the problem recurs.
Just speaking from experience, but I’m not sure the issue is necessarily caused by Modern Standby. This is because I’ve been using Syncthing on Windows tablets for many years. All of them have Modern Standby enabled, but I haven’t noticed any issues that would stop Syncthing from working completely like that. In my case, it just reconnects normally when the devices exit the standby mode.
Based on what I’m seeing so far, I’m leaning heavily towards a Windows problem that happens to impact Syncthing, rather than a Syncthing problem. Until this issue, this laptop has been the most stable Windows machine I’ve ever had as a daily driver.
I’ll continue to watch carefully. I’ve got no sync conflicts, no data loss, and solid backups.