Earlier quoted context omitted.
What is often forgotten, by the early 1930s, the split between SPD and KPD (which dates back to Marx and Engels and the condemnation of the "Bernsteinian revisionism" on the one hand and the SPD not being a revolutionary party after 1903) had become an abyss: to the KPD the SPD was a "social-fascist movement" and the SPD had adopted the three-arrows symbol, which symbolized an equidistance to fascism, communism and m…
The rift dates to WW1, not the 1930s, and considering the three arrows to be a better marking of the rift than the SPD literally giving the order to murder KPD is nonsensical. There was no split in 1903 - the SPD simply had both a revolutionary and electoral faction. And Bernsteinian revisionism wasn't about taking power through elections or through revolution (which is what the SPD took position on in 1903), it was…
So I find it very dubious that KPD and SPD couldn't have made a single united front, if instructions from Moscow weren't towards the opposite.