Ion-avatar & ion-thumbnail display problem

When I use <ion-avatar> or <ion-thumbnail> the image is not displayed instead a white empty is take the place, after I refresh the app I see the images displayed but when I do some actions like navigation that white space is appeared.
how I can fix this problem ?
code snapshot:

<ion-thumbnail *ngIf="user.photoUrl" slot="start">
            <ion-img [src]="user.photoUrl"></ion-img>
          </ion-thumbnail>
ion-thumbnail {
  --border-radius: 50%;
}

g

Is it possible that user.photoUrl is slow to download, maybe slow server, or large file?