Hey there, I have the same issue, regardless which picture I try to upload. Even a picture that worked fine on one occasion couldn't be uploaded to the same template when I tried.
I started having this problem on Adobe Express (Android) mobile recently. Two PNG files that are almost exactly the same in size and design with one uploading and the other unable to be uploaded. No matter what I do with that "unloadable" file, AE will not accept it in my design.
Could you check if the following helps? If not, please feel free to send me a private message with the two files.
Issue
Workaround
Uploading a file from the device failed (Android).
When uploading a file from your Android device, upload may fail when selecting Photos, Videos, Take a photo, or Record a video. As a workaround, you can select Upload from device > Choose file to upload a file from your Android device.