I can't directly comment on how to install a current version, but for anyone with more experience with this device or its sibling, the commit message is (and suggests, to me at least, that TFTP installation is required).
Author: Stefan Lippers-Hollmann <redacted>
Date: Fri May 18 03:49:27 2018 +0200
ipq806x: increase kernel partition size for the Netgear Nighthawk X4 D7800
Starting with kernel 4.14 and gcc 7, the kernel doesn't fit into the
2 MB reserved for the kernel partition by the OEM firmware anymore.
This patch increases the kernel partition from 2 MB to 4 MB, at the
expense of the rootfs, for all supported kernels.
WARNING: This breaks sysupgrade! Flashing a firmware containing this
changed partitioning from an older image with 2 MB reserved for the
kernel partion requires the tftp recovery procedure, thereby losing
This change follows the functional example of the Netgear r7800, but
has not been runtime tested on a Netgear Nighthawk X4 D7800.
thank you for your support, what is strange in this situation is that I've read about many people that successful flash a >18.06 version without any problem with my same hw. It seems that they flash through official netgear d7800 web interface.
In my case I think is a problem of partition, because I successful flash the last 17 version.
I tried with an other laptop (macbook air) with the same result, only the last 17 version work.
BTW now I've noticed that sometimes I cannot go to tftp mode by pushing reset button, after the flashing orange light it comes to white light without flashing.
I don't know why. After several try I can go to tftp flash mode. It seems without any change of my behaviour.