Are you engaging the pto at full throttle ? Some manufacturers say 1/2 throttle .Some say full throttle. I think it has to do with belt slap . There has to be an awful lot of torque on a single belt when the engine is turning 3600 and you engage the electric pto and try to get 3 blades up to speed in a matter of 1 or 2 seconds. You would think it would be best to engage pto at a speed just above idle then increase rpm but Who am I to say ?It's just my half-fast opinion......
Just my half-fast opinion....Fixdiss