I just set up my new Archer AX50. All good except I have a 2TB Seagate external hard drive that I have plugged into the usb port so that I can access this for storage from all my computers on my home network.  I can see and access hard drive wirelessly only if I am connected to my 2.4GHZ.  If I wirelessly connect to my 5.0GHZ, I can no longer see or access the hard drive.  I can however see it regardless on my router utility page, just not seen on Finder (yes I am on a mac).