You may have received an error message that a user’s vocabulary is damaged.
Having too little available storage on the device can cause this issue.
For details on how to check your storage, please go to the following Apple Support Article: https://support.apple.com/en-us/HT201656. Delete any unneeded apps, videos, etc. It's important to have at least 5GB of available storage.
Once you have freed up space, please close Proloquo2Go via the App switcher and force restart your device:
1. Open the App Switcher by either swiping up from the bottom of the screen and then pausing in the middle or (if you have a Home button) double pressing the Home button.
2. Locate Proloquo2Go and then swipe up on the app.
3. To close the App Switcher, tap the screen or press the Home button (on an iPad with a Home button).
Open Proloquo2Go and see if this resolved the issue.
If not, please email support@assistiveware.com and we will continue to troubleshoot.