Once the left takes power, then they fight over who controls the power. Eventually, in most cases, it comes down to the control of one strong man, such as Lenin, Stalin, Pol Pot, Mao, Castro, Maduro, Tito, etc.
It is pretty much built into the system. If the party needs to rule the people, somebody needs to rule the party.
Commie front groups such as United For Peace and Justice used to often bicker about various points with their comrades at the ANSWER Coalition.
UP&J was/is a front for Communist Party USA. ANSWER, Workers World Party.
Don’t forget Hitler and the Bavarian Communists he and the boys took out!