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 [v2.3] (NSFW 18+) 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.