You mean you have the rt-ac68u as node and no 5G?
As I have the rt-ac86u as router and 2 rt-ac68u as nodes and only one of them has 5G.
With beta 2 all of them had 2 and 5g.
After a couple of factory reset and restarts they all have 2 and 5G.
Maybe a something didn't get a chance to start correctly
The RT-AC68U is used as a node.
With 384-19 i had :
Wifi 2.4G
Wifi 5G
Wifi 5G_2
Now with 386-1 beta 3 i have :
Wifi 2.4G
Wifi 5G_2