Error DNS_PROBE_FINISHED_NXDOMAIN after update to V1.0.1.70_1.0.44 of firmware

> Ever since I have updated my AC1750 R6400 router [...]

   Is that accurate?  R6400[v1] or R6400v2?  Look for "Model" on the
product label.  Firmware versions (before, after)?

   If the new firmware causes problems, then I'd consider reverting to
the older firmware.

   Visit http://netgear.com/support , put in your model number, and look
for Downloads.  (For older versions, under Firmware and Software
Downloads, look for "View Previous Versions".)  Find the kit(s).
Download the kit(s) you want.  Read the "Release Notes" file for
instructions.  (In the User Manual, look for "firmware", and,
especially, for a topic like "Manually Upload Firmware to the Router".)
When that fails because of a deficient User Manual, try:

      https://kb.netgear.com/23960

> Could it be that something went wrong with the firmware update? [...]

   More likely, the newer firmware has more/different bugs.

> Or the netgear in access point mode?

> Have you tried the netgear in access point mode?

   Configuring the R6400[vX] as a wireless access point might help.

   Visit http://netgear.com/support , put in your (actual) model number,
and look for Documentation.  Get the User Manual (at least).  Read.
Look for a topic like "Use the Router as a Wireless Access Point".

   Whether that's a good idea might depend on which router features of
the R6400[vX] you actually use.  (And what the Experia Box v10A lacks.)