The main issue, although there were many, was that the engines could not be test fired.

The engines used ablative nozzles, so once you started the engine, the nozzle would be consumed, and any test fired engine would have to be completely rebuilt. So, the soviets only tested engines from each batch, I think it was something like 1 in 4 or 1 in 6 engines were tested. That sounds reasonable until you realize the N1 first stage consisted of 30 engines.

There was basically no way to tell if they’d built a bomb or a rocket until they lit it off. Turns out they built a bomb every time.