ABS problems on honda cb125r

Hi, looking for some advice. Bike: 2018 Honda CB125R (UK) Issue: Ignition ON (engine off) → ABS light is solid (normal) Start engine → ABS light starts flashing continuously If I hit the kill switch → flashing stops immediately Rear wheel locks very easily under braking (so ABS is definitely not active) Speedometer works perfectly Other details: Battery and regulator/rectifier were replaced ~2 months ago Ground and battery terminals are tight Headlight doesn’t dim on crank and doesn’t change brightness when revving Problem appeared recently I’ve done some chain adjustment/cleaning recently It seems like the ABS disables only when the engine is running, not just ignition on. Could this be: Rear wheel speed sensor? Stator AC ripple? Regulator issue? Wiring vibrating when engine runs? Has anyone had ABS flash only with engine running and immediately stop when kill switch is pressed?