R7800 in AP mode- cannot access web console from another subnet

> I set up the R7800 router in Access Point (AP) mode and have given it
> a static ipaddress. [...]

   Ok.

> [...] Also disabled DHCP. [...]

   Pointless?  Selecting "AP Mode" should do that automatically.

> 404 Not Found
> This server does not support the operation requested by your client.

   What, exactly, is looking for what, exactly, (without success)?

> I've searched the internet for this problem and see [...]

   Thanks for the helpful links.

> Is there anyone at Netgear that can finally escalate this issue and
> get it fixed?

   I'd expect so, but an actual support case is more likely find its
way to any such person than a complaint here is.

   I don't generally deal with local VLANs, so I know nothing, and I
can't see what's actually happening in your case, but I wouldn't expect
LAN operations between different subnets to work without involving a
router.  Hence, it's not obvious to me that there's actually a problem
(with the router) to be "fixed".

> Whether or not this issue is caused by disabled functions while in AP
> mode this is a bug that should be fixed by Netgear. [...]

   I doubt that the cause (bug or other) is a "disabled function"; more
likely, I'd say, it's some incompatibility between the expectations of
the relevant HTML and those of the user.

> [...] I can't believe they still have not addressed this issue.

   That's easy to explain.  How many users of this consumer-grade device
do you think might be affected by such a problem?  With the backlog of
more common bug-reports which Netgear must have, I'd be amazed if
anything like this ever bubbled to the surface.