If you experience areas of your iPad kiosk that are not showing text where you might typically see black on white text, the iPad could be in "Dark Mode".
This is used where you want to use the iPad in low light or reversed display conditions. This functions is not required and should be disabled.
iPad Settings > Display & Brightness
Toggle "Light" mode
You should also make sure brightness is set to 100% and auto lock is off.
For more information get in touch with your support team.