Steps to reproduce:

1. Take 3 (or more) interesting pictures of at least 2 MB (for instance pictures of cars or houses. If you need I can also provide many pictures, just send an email to the address found here).
2. Get a slow Internet connection by installing the Throttly app and setting it to Good 2G 450kbps↓ 150kbps↑.
3. In your gallery app, select the 3 (or more) pictures, tap Share, then select the Commons app.
4. As soon as the upload starts, turn off your screen and do not touch your phone for 5 minutes.
5. Some of the pictures will probably fail to upload.

Many other apps always upload reliably (for instance Gmail with attachments) even with slow Internet connections, even the Commons browser-based uploader seems to perform better, so hopefully we can fix this.

Possible strategy:

1. Reproduce the issue with the Android Studio debugger (or similar), find out what the exact error message is.
2. Based on the error message, change the app's network parameters, such as timeout or buffer sizes.
3. If still not reliable, implement a retry loop (for instance try again 3 times).

Measuring improvements:

• Percentage of failure with the reproduction steps above, as of 2023 January 12's master branch:
  • 1 failure out of a 3-pictures set upload on fast WiFi: 2 occurrences
  • 2 failures out of a 10-pictures set upload on fast WiFi: 1 occurrence
  • 6 failures out of a 9-pictures set upload on fast 5G: 1 occurrence
  • 0 failures out of a 2-pictures set upload on slow WiFi: 1 occurrence

Some uploads get stuck (no progress despite the progress bar showing an animation). Among those stuck, some file have actually been uploaded already, some not.

Aggravating factors:

• Brief network disconnections, for instance when entering an elevator for 1 minute, seem to make uploads less reliable. I have not measured this theory but this could be investigated by putting your phone in a metal box (use a ping chart app to verify)
• I had many successes uploading from the custom picker, and many failures uploading by sharing from the gallery. There might be something about the app going to the background, or something other about activities, that might have an effect on reliability.

Recent Google Play comments:

• "Not a single photo is uploading even though i tried a dozen times"
• "50% of uploads are failed"
• "fails to upload pictures without saying the reason"
• "I can't upload photos. They all say failed. Before it worked fine"
• "Photos cannot be uploaded"