Missing alt content

[dtroode]

After processing image, I get a figure with figcaption, but all content from alt in figcaption:

<figure>
    <img src="image.png" alt="" loading="lazy" data-src="image.png" class="lazyload" width="1000" height="1000">
    <figcaption>Caption</figcaption>
</figure>

I expect, that alt should have the same content as figcaption.