Hisense 3.1 h3100 keep going out of sync

I have a LG C3 and just bought a 3.1 soundbar, a hisense h3100. The soundbar is connected to the tv via hdmi and the subwofer connects via BT.

Sounds starts fine but after either a few seconds or a few minutes the audio inevitably clips and then it goes out of sync. No idea how to fix it