Hi guys, I have the same problems with my TV LG 55LB670 ( Italy, firmware 4.32.20 ) and Soundbar LG NB4540 wireless connected.
The TV is connected to my wireless router @ 5Ghz but I still experienced sound drops / interruptions with soundbar about every 30 minutes.
Sometimes, when I turn ON the TV, soundbar is not connected automatically and a popup from tv asks if I want to change sound output.
I hope that some firmware update could fix it, it's frustrating. If anyone solve this issue please let us know. Thanks