Proform smart pro 9000 treadmill speed fluctuates, inaccurate

I've had this treadmill a year now and on manual or when using ifit the displayed speed is inaccurate. This started a week ago suddenly. At low speeds it isn't as noticable (3mph is equivalent to 3.5mph or so) but at high speeds the difference is noticeable (6mph is around 8 mph).

The belt speed is always faster than displayed and occasionally the belt will speed up for a few seconds (slight increase). All indications point to speed sensor issues based on reading forums but I'm not sure where the speed sensor is on this model. Does anyone have suggestions or troubleshooting tips? I can run on it still but would like to use it on ifit.

Thanks!