editing grace period (default 5 mins) if you enabled
download remote images to local then all the external images in the post will be downloaded locally. If system unable to download the image then “broken link” icon will be replaced with external image.
Also if the download is successful but image is larger than
max image size kb then “large image” icon will be replaced. And it will be linked to that large external image.
Yes, mostly it is not possible for Google Play Store to have broken thumbnail image. So it may happened because of connection issue. In rare cases like this you can click “Rebuild HTML” button then it will be fixed mostly. (Anyway I will improve the code to handle this situation well).
As I told system will try to download all external images.
Because you edited the post or clicked “Rebuild HTML” or somehow that post’s rebake is called.