Glide - Serving cached Images converted to webp

Hi,

i want to improve my Site Performance and use webp-Images. But the conversion from jpg to webp by using the glide tag isn't working.

Here's my code:

<picture>
    <source
        media="(min-width: 1440px)"
        srcset="{{ glide:url width='1600' format="webp" }}" type="image/webp">
    <source
        media="(min-width: 1440px)"
        srcset="{{ glide:url width='1600' }}" type="image/jpeg">

    <source
        media="(min-width: 1024px)"
        srcset="{{ glide:url width='1400' format="webp" }}" type="image/webp">
    <source
        media="(min-width: 1024px)"
        srcset="{{ glide:url width='1400' }}" type="image/jpeg">

    <img src="{{ glide:url width='750' }}" alt="{{ title }}" >
</picture>

I've tried to change the conversion format to png and it worked without a problem. But with webp the page loads for a while (just like it would generate the cached images) and when finished, the src- & srcset-Tags are empty and only the jpg-Image is shown.

Thanks in advance!

Nico