qngnht I ran into this a while ago too as I recall... I believe I had varying success depending on the network I was testing things on. For instance, while at work, while prototyping something for work, I'd experience what you are seeing. However, at home, on my home network, I would not.
However, even at home, I was never able to get past the following -- WebRTC connections being dropped when an app (AKA the server) goes to sleep... There is about a 1 minute window (depending on Browser WebTRC implementation) before a minimized app will kill the connection to all of it's peers (for battery saving purposes I'd imagine)
Good luck to you!