If the bunkers doesn't have light inside then it is used as an indicator that those bunkers won't spawn HT on defense which is very helpful during scouting for Multiplayer battles as it is an easily noticeable indicator than the smoke coming out of the chimney.
Suggestion: Fix Bunker level 6 to add the additional indicator of light inside like all the previous levels of bunker.
Suggestion: Fix Bunker level 6 to add the additional indicator of light inside like all the previous levels of bunker.