Suggestion: Add an event
Left-wing militants marching
When KPD’s popularity surges to more than 30% and higher than the SPD, it should be able to rapidly grow RFB and attempt to launch a communist coup attempt to overthrow the state, especially if the Nazi support is high. To trigger this event, you will need to make sure KPD has higher support than all other parties, including the Nazis, and you have implemented austerity policies that impoverished the working-class and the unemployed.
If you lost or do not resist the takeover of the commies, the KPD would turn Germany into a totalitarian Stalinist dictatorship and start violent purges and massacres, similar to Stalinist USSR, and begin to help Moscow sponsor more Stalinist parties and regimes in Europe.
If the unions declared independence due to your anti-worker policies, they might side with the KPD instead of the SPD
