So please ensure that you firstly record the Token value for each device, as should be indicated in the 'TOKEN' field within 'Settings > TPControl'. This will ensure that at least the devices can be re-registered should that be required.
Now, please try the following:
1. Turn on the 'Reprocess TP4 file' option in within 'Settings > TPControl > Developer Settings' on the device, relaunch TPControl and when prompted by 'Settings were changed' press OK.
If you still have trouble, there is likely an on-device data corruption which may require uninstalling/reinstalling TPControl. However, before doing so please confirm that you have the TOKEN value and that all relevant Settings and TP4 file information is available for the device. This information, if not already, can and should be configured within TPCloud (http://tpcloud.touchpanelcontrol.com) for the TOKEN value. Once this has been done, move on to option 2.
2. Turn on the 'Clear User Pages' option in within 'Settings > TPControl > Developer Settings'.
NOTE: This removes the UI file, meaning that the TP4 file will need to be reinstalled.
Again, if the Settings and TP4 file for the TOKEN value have been configured and enabled within our online TPCloud service, then this greatly simplifies the restoration process, enabling all information needed by TPControl to be restored without needing to attend site (assuming your device can access the Internet).
After clearing, turn on the 'TPCloud update' option available in 'Settings > TPControl' on the device, relaunch TPControl and when prompted by 'Settings were changed' press OK. The device will download relevant information from TPCloud as configured.
If after the update you still are having trouble with TPControl reverting to the desktop, then it is likely an application corruption has occurred, in which case you will need to uninstall TPControl. Before doing so, please turn on the 'Token Registration' option, relaunch TPControl and record the 'TPC User ID (email address)' listed in the dialog. Then, return to desktop, uninstall TPControl and reinstall via the AppStore on the device. Once reinstalled, launch TPControl and once the first launch has completed double-tap the UI to present the 'Token Registration' window (or turn on the 'Token Registration' option as above). Enter the TPC User ID and Token in the fields presented and press 'Submit'. If prompted, press Submit again, otherwise, if the dialog mentions that you need to Deauthorize, please reply to this ticket and include the TPC Device ID (available in Settings > TPControl), and I can assign that to the relevant Token to get the device relicensed. After that, you can perform a 'TPCloud update' (refer 'Settings > TPControl > TPCloud update') to restore the Settings and TP4 file from the above steps via TPCloud.