When I try to exit from the ad the screen goes blank. I have tried clicking on the cancellation x, using the back space, and opening the ad to read more, but all I get is a blank screen. The only way to exit is to close all open windows on device (Android tablet) and begin again. Very irritating.
What app version are you using?
Sometimes older versions have bugs, sometimes new versions are released and are very un-tested and buggier than before (especially for new features).
You, the users, are their ALPHA / BETA testers...
You want to report issues like this with some screenshots under "Help" with ther green "Submit bug report" button.