Thanks for those details! There isn't an obvious reason why Central is responding in this way, so we'd like to try to reproduce the problem. Would you be open to sending us the odk folder? To do that...
- Install Files from the Play Store. https://play.google.com/store/apps/details?id=com.marc.files is the direct link.
- Switch from icon view to list view for easier navigation.
- Tap on "Android", then "data", then "org.odk.collect.android".
- Long press on "files" folder, tap on ⋮, then tap Compress icon.
- Long press on "files.zip" file, tap on ⋮, then tap Share icon.
- Chose Gmail, it will create a new email with files.zip. Send the email to support@getodk.org.
- When you are done, long press "files.zip" (not files!), tap on Trash icon. Click OK to confirm.