A bunch of settings missing from Asus AC66r professional tab

I was trying to optimize my router for max speed, set the preamble to short on the 5ghz professional page, and now I'm missing a bunch of settings on that page. The option to set the preamble is gone, there were beamforming options that were there that are gone, and repeatedly logging in and going to that page, every now and then it will show the entire list of options for a split second while loading, but then after finishing loading only displays about half of them.

What's going on? Is...

A bunch of settings missing from Asus AC66r professional tab