auto stop start screeching

[Howy]

Hello, so when the stop start is engaging the vehicle does a harsh screech and then stalls, the accessory belt tensioner pully is being pulled into the aux belt itself (see video), do we think this is just a belt issue or a tensioner issue? thanks

FORD TRANSIT CUSTOM V362 CAMIONNETTE 2.0 ECOBLUE MHEV
(04/2012 - Today) Diesel/électrique > 2.0 EcoBlue mHEV (96 KW, 130 CH) 19