They are not on the same lan. Thats when I speak about “external” nodes and so on. Two separate lans, and I cant control if they have fully working ipv6 global addresses or not.
I have now manually set from default listening entry to tcp4://… for the linux machine and restarated both linux and win10 syncthing
now they connect again. before they would not connect not even after both processes on both ends had been restarted
i strongly suspect that those discovery servers and the bulk data that is being transfered, registered or looked up on or with the help of discovery servers is severly affected by the addition or prefering of this new kcp method or similar to this.
i am only rather a layman and didnt look at your source code but this is what i suspect after looking at all this trouble.
machines dont have trouble when being on the same lan, i have several other machines every now and then every few days that are showing up physically in the lan of the linux machine (main headquarter place so to speak).
some machines are external most of the times, like this win 10 machine for example.
some other win10 machine (surface, lap…) or some mac are sometimes present in the lan and sometimes external.
thats all i can say. the connection logic is flawed with this current release.