I have a similar problem, except that sometimes the program starts and the connections work just fine, sometimes they don’t connect to specific machines, sometimes they don’t connect to anything at all.
There are 7 Windows 10 x64 desktops, 1 Windows 10 x64 laptop, 1 Windows 7 laptop, and 2 Synology DS214play NAS devices.
There are no software firewalls, except for Windows default, but syncthing.exe has permission to open ports in all machines. At home I use UPnP NAT. At work I don’t know about external firewalls, but apparently they are not blocking any ports.
I don’t know exactly when the problem started, but I think it started with the version 0.12.x family.
I was going to install the builds posted here now, since the maching I’m using now (one of the Windows 10 ones) was sitting here for hours without connecting to anything. But just before I did that I went to check the state of Syncthing on one of the NAS. Since the interface was not loading properly (some stuff, like connection status not loading, others, like folders, loading fine), I killed the syncthing process on it.
When I did that, the Windows 10 machine I’m using immediatelly started connecting to the other machines and it’s now working just fine. I even restarted the NAS process and it is also synching again.
So, apparently, one single device may do something that freezes most or all the others’ connections, even those not related to it.
I will wait until it happens again and test these new builds and write the logs files. Anything else I should look into?
The workaround for now seems to be restarting syncthing on all devices until the culprit is found.
Since this problem is not Windows 10 related (apparently) should I open a new topic?