May be just a little bit more training during the driver change, they are not used to this homologated seat and belts. See at 0"27, JJ in the pits "adjusting" the shoulder straps but further probably opening the buckle something I don't think he's allowed to do before complete stop:
https://www.youtube.com/watch?v=Ct5PO7Hlfy8
Transparent adjustable addition to the Gurney more visible here:
https://www.youtube.com/watch?v=bVFaoWoiQ_k And on the top of the rear window too…