GIFs inserted in to a page will not autoplay and will display as static images

Summary

Newly embedded GIFs in the page will not autoplay or animate

Steps to Reproduce

1. Create a new blank page in Confluence
2. Add animated gif to a page
   You can use bellow gif as an example:
   

Expected Results

• gif autoplay on the page once the page is saved as it was in previous Confluence versions

Actual Results

GIFs remains static and does not animate unless previewed
GIFs inserted into pages prior to upgrade continue to autoplay

If checked on source editor, thumbnail preview can be seen to be added to the image, preventing autoplay:

ac:thumbnail="true"

If the page is inspected, the same thumbnail can be observed under image class

<img class="confluence-embedded-image confluence-thumbnail" ....

Notes

• The Issue is not observed for large gifs, only for small icon size
• The issue is not observed when copy pasting the GIF directly from clipboard into Confluence editor
• The issue is not observed on Confluence 5.10.*
• The issue is not observed on Gifs inserted prior to the upgrade

Workaround

• Editing image and applying Effect will result in image autoplay correctly and no actual effect applied
• Edit the page and ensure that the GIF is not on thumbnail size. GIFs on Original size will work correctly.
  
• Using Confluence Source Editor to remove thumbnail tag from gif source: ac:thumbnail="true" will allow autoplay