I also have this issue with v0.12.1 alpha. Was able to log in to iOS and Android versions of PE on a local server without any issues. Directly after the update this was not possible. Have already tried to set static IPs and made certain that local server multiplayer is set to on. Would love to see this fixed!
I was getting the same problem with the launcher not working. it had an update this afternoon and is now not even generating an error for me