Remote side unexpectedly closed network connection

Hi. First time dabbling with OpenWRT and I'm still learning.

The issue I'm having is when I try and execute sysupgrade -v sysupgrade.bin PuTTY gets disconnected which I assume usual as it wipes everything and reboots the router but once the router reboots I cannot access it via browser 192.168.1.1 and I'm back to square one.

My router is Zyxel LTE5398-M904.

Appreciate all your help in advance.

I'm getting stuck here..

Depending on what you upgrade with there could be no LuCi at all only SSH.

So after upgrade try SSH.

See: https://openwrt.org/docs/guide-quick-start/developmentinstallation

Picture from terminal shows sysupgrade process which reboots OpenWRT right after disconnecting all dropbear ssh sessions.

You have installed a snapshot image. Read the link for instructions how to install Luci, which is not installed by default in snapshots.

https://openwrt.org/faq/can_not_connect_via_webbrowser