Nest timeout using android marshmallows. Android <6 works. something has changed?

Question

my application needs to connect to a Wi-Fi network that does not have an Internet connection and open a socket for port 9402.

After I upgraded my Nexus 5 to Android 6, it stopped working (socket timeout). My wife's android 5 phone is still working.

Does anyone know if something has changed regarding this?

thanks