Out of curiosity I’ve tested this and I can confirm that the problem exists: avatars from dicebar are not shown in iOS app build (but are shown on web).
I’ve investigated the issue a bit and it turns out the problem is related to displaying .svg images. For example:
The last one generates JPG files, unlike Dicebar and UI-avatars. So I can conclude that the problem is related to svg. Additional proof for this - when I try to use static SVG file URL (https://upload.wikimedia.org/wikipedia/commons/2/2f/Google_2015_logo.svg), it works in PWA, but still doesn’t work on iOS.
I believe that only Adalo can fix this so submitting support ticket is worthwhile: Submit a Support Ticket