i had a few broken spokes recently on my cargo bike with disc brakes . one at a time over some weeks both drive side and non drive side on the rear wheel . my symptom was also spokes breaking mid spoke . i also had never experienced a broken spoke in many years of cycling . i did some research and found it could be de-tensioned spokes / spokes losing tension over the 7 years i had been riding this bike. i re-tensioned all the spokes and so far it's fixed the problem