The resistants and communists act like a bunch of amateurs
I guess the resistance did not spring up overnight, and many enthusiastic young men joined, but some of their actions and mistakes would have got them apprehended within hours, if not minutes. The communists being older should have known better.
Rules for clandestine operatives:
1. when being asked by unfamiliar chatty coworkers/recruits, tell them they ask too many questions and shut up.
2. When hiding out in the forest do not light fires in the open. The smoke can be seen and smelled from miles away.
3. When attacking a German truck (Season 5 episode 2) make the soldiers get undressed so as not to get blood on their uniforms, then quietly cut their throats rather than waste bullets and make a racket. Collect up the uniforms and weapons for later use. Bury the bodies. If it is possible to hide the truck somewhere, take the truck, otherwise, disable it. Try putting the bodies in the truck, pushing it down the ravine and setting fire to it. It might be seen as an accident at first.
I could list many more faux pas. From the series it appears the Germans lost the war because of the imbalance of weapons and materials rather than the skill of the resistance.