OpenWRT webGUI is not opening with an error message

Hi I'm trying to debug an issue related to webGUI problem facing.
It stop working with this error.

/usr/lib/lua/luci/dispatcher.lua:448: Failed to execute arcombine dispatcher target for entry '/admin/network/network/lan'.
The called action terminated with an exception:
/usr/lib/lua/luci/model/network.lua:1066: attempt to index upvalue '_ubus' (a nil value)
stack traceback:
[C]: in function 'assert'
/usr/lib/lua/luci/dispatcher.lua:448: in function 'dispatch'
/usr/lib/lua/luci/dispatcher.lua:195: in function </usr/lib/lua/luci/dispatcher.lua:194>

After rebooting device working back to normal and some random period of time GUI Stock with the above error.

mainly two type of error I noticed till now one is above and second is here.

/usr/lib/lua/luci/dispatcher.lua:448: Failed to execute function dispatcher target for entry '/'.
The called action terminated with an exception:
/usr/lib/lua/luci/sauth.lua:87: Session data invalid!
stack traceback:
[C]: in function 'assert'
/usr/lib/lua/luci/dispatcher.lua:448: in function 'dispatch'
/usr/lib/lua/luci/dispatcher.lua:195: in function </usr/lib/lua/luci/dispatcher.lua:194>

Will anyone please help to solve this issue?

Sounds like the ubusd daemon is crashing or not accepting connections.