Thank you for the question.
The answer is quite simple. Those groups are being used by the anti-election powers that be. Their reasoning is this: if the country is plunged into chaos, it can't hold elections. Therefore, they create rebel groups, on both sides, such as those in Bas-Congo that killed Bundu dia Kongo followers, those in Kasaï that killed members of Kamuina Nsapu, and those in Kivu. It was the Alliance of Democratic Forces, the same militia fighters who speak Kinyarwanda and Kirundi and who are in cahoots with the current government.
The government of Congo is the one funding the atrocities happening all over the country, in order to strengthen its grip on power and justify the decision not to hold elections.