Yeah I tried it on both motors and without the second ESC - always the same thing. Seems like the neutral position is not detected properly and changing the deadband via the programming card has no effect as well. Don’t know how to fix this now I am using 150A XCar beast ESCs - my first one worked perfectly fine (I had to cut off the fan though - that thing is just annoyingly loud) and onle the “new” one gives me headaches.
Ok I might have figured it out. After reconnecting the red wire the second ESC also turned on whenever I switched just one of the ESCs on. However this way the problem persisted. When I turn on both at the same time however the jittery ESC works fine (at least it did on the weekend ). Thanks everyone for helping me out here.