Blades engaging intermittently/surging: Husqvarna zero turn Z246, Kaw FR600V AS 18,

Hello there, Need expert advice please. I ran over a garden hose the other day and v belt and tension spring came off. Couple of hours mowing next day no problem, until belt slipped and spring came off again (ran out of juice and mower stopped just before this). I know, I'm hoses and fuel challenged but it had been a long day :) Reattached spring and threaded belt again and blades engaged. Blades ran at normal speed while stationary and then started intermittently loosing power and surging back to full speed at different time intervals while mowing at different heights of deck and lengths of grass. I can't establish a pattern, seems random. Tested PTO switch all good, tested earth all good, tested resistance on clutch all good, fuse all good. Did find left side lever safety switch was loose and wondered if this could be the problem. Tested switch for continuity, all good. Tested also while running by engaging blade and wiggling Left side lever to see if loose safety switch could be causing clutch to surge on and off and slip the belt due to the vibration. I will order a new belt tomorrow and try that, guessing old belt may be stretched despite increasing the tension. Hopefully it will run as normal with a new belt, but I think there might be an electrical fault somewhere and I'm hoping someone may have some ideas for me. Please note, this is my first multi meter ever and the breadth of my electrical/mechanical knowledge is close to zero, so please advise in lay terms. TIA, Amanda