Has anyone else had problems connecting devices to the MESH network?

I have a number of X20 (wried backhaul) with one as the router and additionally a pair of XE75's set up.

Over the last couple of years of ownership I've not encountered any problems but I've recently tried to separately connect two LG USE6S soundbars and am not having any luck.

Conenction type is WPA2, Fast roaming and beamforming enabled.

LG app on the iPhone connects to the soundbar which after failing to connect to the network comes up with the message "Failed to connect Wi-Fi to the Soundbar. A router was found but could not connect".

Any advice gratefully received.

Many thanks in advacne.