It occurred on 1 device only, because there is no other RUT230 to update. I can reset the device, it is not in real operation at the moment, but prefer not to erase the configuration to often ;-).
I just found a similar error also in the page Status > Network > OpenVPN
/usr/lib/lua/luci/dispatcher.lua:518: Failed to execute template dispatcher target for entry '/admin/status/netinfo/openvpn'.
The called action terminated with an exception:
/usr/lib/lua/luci/template.lua:105: Failed to execute template 'admin_status/netinfo_openvpn'.
A runtime error occured: /usr/lib/lua/teltonika_lua_functions.lua:365: bad argument #1 to 'char' (integer expected, got nil)
[C]: in function 'assert'
/usr/lib/lua/luci/dispatcher.lua:518: in function 'dispatch'
/usr/lib/lua/luci/dispatcher.lua:263: in function </usr/lib/lua/luci/dispatcher.lua:262>
I will first try to update the same firmware again, then downgrade to 01.02.3 to test. I will see if the described method makes any difference.
Any other suggestions are welcome :-)