Image size set to `1w` if sizes is set to `100vw`

Somehow 100vw will be converted to a 1w and 2w url and I don't understand why.

Local

<img
  sizes="(max-width: 640px) 100vw, (max-width: 768px) 50vw, 400px"
  srcset="
    /_ipx/w_1/twitter-image.png     1w,
    /_ipx/w_2/twitter-image.png     2w,
    /_ipx/w_320/twitter-image.png 320w,
    /_ipx/w_400/twitter-image.png 400w,
    /_ipx/w_640/twitter-image.png 640w,
    /_ipx/w_800/twitter-image.png 800w
  "
  src="/_ipx/w_800/twitter-image.png"
/>

Storyblok

<img
  sizes="(max-width: 640px) 100vw, (max-width: 768px) 50vw, 400px"
  srcset="
    https://a.storyblok.com/f/23194/3000x2000/09das0980/image.png/m/1x0     1w,
    https://a.storyblok.com/f/23194/3000x2000/09das0980/image.png/m/2x0     2w,
    https://a.storyblok.com/f/23194/3000x2000/09das0980/image.png/m/320x0 320w,
    https://a.storyblok.com/f/23194/3000x2000/09das0980/image.png/m/400x0 400w,
    https://a.storyblok.com/f/23194/3000x2000/09das0980/image.png/m/640x0 640w,
    https://a.storyblok.com/f/23194/3000x2000/09das0980/image.png/m/800x0 800w
  "
  src="https://a.storyblok.com/f/23194/3000x2000/09das0980/image.png/m/800x0"
/>

Start by reproducing the generated srcset from the Local example and compare it with the Storyblok output. Trace the responsive image-size calculation that turns 100vw into 1w and 2w. Done means the generated widths correctly reflect the sizes value without breaking the other listed widths.