WebP JS only works on some pages

Hi

If you look a this page, the webP is working properly for the images: https://www.truckpages.co.uk/trucks-for-sale/2014-daf-cf85-410-hookloader-direct-operator/

Whereas on the listings page https://www.truckpages.co.uk/trucks-for-sale/ it is not (sorry, the truck may have moved off the first page by the time you see this).

But in any case, it appears that none of the trucks on this page type are using webP. Could there be a conflict somewhere?

I have cleared all cache files and viewed with Autoptimize off but this makes no difference.

Not all of the files have been processed and given a webP version as there are over 500,000 to process and it is taking a while.

Many Thanks

The page I need help with: [log in to see the link]