The thumbnail doesn't update after the image URL is changed on edited posts. This also applies to changing the web URL for article posts and the thumbnail for that remaining the cached version. Tapping on the thumbnail will go to the proper image or article; it's just the thumbnail that doesn't update in 366.

EDIT: Uhh and the feeds aren't updating from the cache either? After I posted this, I don't see the post when visiting the Connect community. This issue was definitely introduced recently.

EDIT 2: If you do a thumbnail preview and then tap on the comments/feed name in the menu at the top, the feed/comm will reload but the preview is stuck on screen until the app is reopened. Applies when you're on a feed or in a post and long tap to preview.