Seems to be caused by a number of things, the biggest ones being install permissions (especially now with the new sideloading restrictions Google implemented) or creating a new APK for the same game with a different keystore than the original. I'd make sure those two things aren't getting in the way before anything
It can also happen because of a corrupted APK, at which point the logs folder can tell you if anything's wrong. You can send me the log files at contact@kagurarpg.com if you want me to take a look for you, but it's more likely one of the things I mentioned above