File Transfer: promise resolves, but download incomplete

Hello all,
a problem occurs when I try to use Ionic Native File Transfer plugin in my app.
For offline support I need an image to be downloaded to the mobile filesystem. Here is a snippet from my code:

const fileTransfer = transfer.create();
            Observable.fromPromise( + encodeURI(url), target)).subscribe(fileEntry => {

I wait for the promise to resolve, wait for all download streams to complete and then switch ngIf with an isInitialized event to show the images.
I thought that the promise resolve will trigger as soon as the image was completely downloaded but that seems to be wrong.

*ngIf="(isInitialized$ | async) && campaigns.length === 0"
<img src={{getImage(campaign.image)}} alt={{campaign.title}} showOnLoad/>

When I start the app and the images get loaded from a server, after all file transfer promises are resolved, the images will be rendered incomplete (green or gray, sometimes rainbow bars at the bottom of the images). When I refresh the page some seconds later (without triggering a new download), the images are rendered correctly from the file system. Is there an event to listen for, that emits when the image is 100% downloaded? or does somebody know a better plugin to use?
The problem occurs on both platforms, iOS and android.

What Promise are you referring to please? There’s no mention of Promises in the plugin’s types file. returns a Promise that resolves to a FileEntry object.

But are you sure it’s Promises/A+ compliant? Observable.fromPromise() requires that. Ionic Native just slaps a type on it in half a line of code.

I mean, maybe it’s compliant, but I can’t see why at a glance. So I wouldn’t use Observable.fromPromise with it. Do you still have the issue when you treat download like a thenable instead of like a fully-defined Promise?