Just did several tests with @Southside @viv and @ustulation. It all ended up in a hangout and we’ve tested several builds for the safe_vault binary. As it turns out, connecting from windows-to-windows gives trouble on the network. Connecting from windows-to-linux isn’t a problem. Linux-to-linux isn’t a problem either.
@Viv made a build with the proposed update to mio-6 and I was able to connect from windows home PC to an AWS windows machine.
I guess it’s case closed, this “FailedExternalReachability” probably won’t show up in TEST 12c. Will make it more easy to start a community network later on as well ;-).