So I reverted back to the 25124 firmware on the et8, but it didn't work. Still no 6e. Given what was said about using the axe11000 as the node and still no 6e on the node, it leaves me to believe that both the router and the node have to be reverted....
I'm having the same issue with axe11000 as main router and an et8 as node via 2.5GHz Ethernet backhaul. Only the axe11000 broadcasts 6GHz. I have this same exact setup at another house with identical problem.