I have a Deco x50 5g Router with four M5 extenders. Everything was working well until the mobile signal was upgraded to 5g from 4g in the area. I am using Three UK SIM. Nothing has changed in terms of location, the upgrade from 4g to 5g was automatic after the weekly reboot of the router. I am now fining that the wireless netwrok is lagging when connecting to the M5 extenrs but seems to be better connected directly to the router. A speed test connected to the router shows anyhting up to 450mbs downlaod and 50mbs upload. When conneted via an M5 that speed reduces to almost nothing in some and doesn't remain stable on testing.

The connectivity between router and M5's remains good and doesn't drop.

I have diabled QOS and UnP. 

I was asked by technical support to apple a cell lock but on my app this is greyed out and won't allow me to enable.

I have other Three UK Sims is mobile phones and don't have the issues.