Hey! Try re-installing the app because this issue seems to be related to your handset, as no one else has reported this before.
Viewing post in KonoSuba The Harem Adventures comments
For some reason, every time I reinstalled it, it still had save data, even after deleting the old data. Loading the same save still didn't work. I tried a new game and that seemed to work. I'm not sure if I tried an old save before or not, but doing so now it worked, so I at least managed to save some time. I'm guessing it was an issue that stuck with that save. Hopefully this means it's fixed now, especially when I get back to where I was.