I can confirm this is a power issue I used a 5v powered hub and that solved the disconnection problem, I then had to manually bridge the interfaces using the ‘advanced’ option.
before starting ensure that your stick and router are on separate ip ranges as they come on the same ones by default. I set the stick to 192.168.7.*
from normal user interface click on advanced, log in, from the top menu select ‘Network’ then ‘Interfaces’ then click ‘edit’ on the ‘Tethering’ section then click on the ‘Physical settings’ tab and put a tick in the box at the top ‘Bridge interfaces’ then in each of the boxes for eth1, eth2 and ‘Wireless network’ (Wlan) this will link the 4G stick to the LAN port and the WiFi