I never had this issue until I subscribed to JetPack Premium. ☹
1. I go to the Media section.
2. I upload pictures from my phone’s Gallery.
3. I wait a few seconds up to a minute after it failed, then I pull down the page to refresh it.
4. The app will show the uploaded files. No need to press on the “retry” button manually!
5. I delete the failed uploads by pressing on the trash bin icon.
6. I insert the pictures in a draft post from the WordPress Media gallery.
P.S. Tested on Android and iOS