This issue only happens if 2 following conditions are met:
The file is uploaded through File column type. (Image files uploaded via Image column type worked fine for me)
The selected file from android file picker is an image file. (Other file types like PDF or JSON can be uploaded from mobile without any issue)
This suggests that the issue lies in how Appsheet mobile app handle file upload differently between Image and File column type, and also between media and document file type.