Hey @musilda
It looks like a conflict between LazyLoad and WebP display feature (this code is a replacement from LazyLoad).
If you don’t use Cloudflare or CDN (or both), it would be ideal to use rewrite rules method to deliver WebP as it would work just fine. I can’t see any trace of CDN/Cloudflare so it would be the best thing to try at first.
Other than that, you might try to use alternate LazyLoad plugin in order to avoid the conflict.
It looks like you use Flatsome’s LazyLoad, you can try Rocket LazyLoad plugin (free plugin) as it should work just fine.
But rewrite rules method should do the job so let me know if that’s the case.
Best Regards
Marko