After migrating from on-premise to Cloud, large images doesn't render properly in pages on Cloud. Instead, 'Broken image' icon appears. When checking its properties, effects tab show this: 

This image is too large to apply effects. Please make it smaller (less than 4,000,000px in total dimensions) and try again.

The affected images were larger in size (100 MB+) and had a custom set size.
The storage format for the page shows that setting a custom size for the broken image below. Broken image issues occur for both width and height.

<li><ac:image ac:thumbnail="true" ac:height="150"><ri:attachment ri:filename="PicName.png" ri:version-at-save="1" /></ac:image></li>

Workaround:

• Convert the legacy pages to new editor experience.
• Downsize the attached image to below 99MB size and replace the image.
• After the migration, go to Cloud instance, and open the page in edit mode, click on the broken image in edit mode and choose "Properties" then click the 'original size' (change it to an original size instead of having a scaled size).

  <li><ac:image ac:thumbnail="true"><ri:attachment ri:filename="PicName.png" ri:version-at-save="1" /></ac:image></li>