How to disable Wireless AP mode

> On the "ADVANCED home" page for my router, under both 2.4 ghz and 5
> ghz it lists Wireless AP as being on, despite not being enabled in
> ADVANCED>Advanced Setup>Wireless AP. How do I disable Wireless AP?

   Two different things: "Wireless AP" and "[Wireless] Access Point
Mode".

   Strictly speaking, a "wireless access point" is the part of the
wireless router which handles the wireless communication.  The R6400 has
one for each frequency band, and that's what the ADVANCED > ADVANCED
Home page controls.  Disabling an AP switches off that radio, but
doesn't affect other router functions.

   Wireless access point _mode_ is a mode of operation which disables
most/all of the router functions, leaving only the wireless access point
functions.  That's what ADVANCED > Wireless Access Point : Enable Access
Point Mode controls.  If that box is unchecked, then your R6400 should
be in full-function router mode.

   What would you like the R6400 to do?