I think it is due to your drive sprocket and rear wheel sprocket alignment due to the fat tire bike. I have a similar issue my bike is small so I have an imperfect tilt to the motor at about 5-10 degrees. What it does is make the chain twist slightly and want to jump off the drive sprocket. For irregular builds, we have to juggle possible alignment to two sprockets versus one (rear). I have a chain tensioner both at the drive sprocket and rear sprocket to compensate the imperfect tilt. It works great but ideally you would want to check your alignment and try to fix it and not use two tensioners to fix the imperfection. The top chain has tension and usually is fine, its the bottom chain right at the rear sprocket where most of the problem comes from. If you cannot get the imperfection hammered out and the chain is jumping from the rear sprocket, then place the chain tensioner as close to the rear sprocket as possible and the roller as low as possible. This will provide the best guide to the sprocket. again, ideally you fix the imperfection but u can always brute force it with two tensioners. see pic
** that nice brutalization of English...