Have you checked all the configurations from your Collect android app
to see if there are any issues? Maybe you will need to check the following:
- Date and time of your device. If there is an issue with the same you may have syncing issues.
- URL settings.
In addition to this also check out that the project that you have collected data for is still there on the server. If the same is missing you may have issues with syncing your data. Maybe this post discussed previously should also be helpful to investigate your issue: