@Anonymous User First we could try to check if the refresh token is expired - when the refresh token is expired and the user is still in the project, the user can still press the send button, but nothing happens. To rule this out, you can close the project and go back to 'My workspace' page, click the user thumbnail, and see if there's a warning message to ask you to re-enter your password.
If this doesn't help, we will need to check the app's logging to see what went wrong. To enable logging, go to the app menu again, press the hold the About option for 6 seconds until the Reset option shows up. Now click the Settings option, scroll down, switch on Logging. You will notice a floating icon shows up now, that's where the logging info is stored. Now you can repeat the workflow you described in the issue and try to send the records again from your device. If it fails again, click on the floating icon and check the 'Upload' tab. Take a screenshot and send it to us (or if anything went wrong, messages will show as red on this page now).
Let me know if you find anything.