Thanks for the comment!
Yes, I had mobile game in mind while designing the game but I decided to build it as a WebGL because a) I have no previous experience in developing for mobile and b) it provides easier access for others to test the game. However, I have understood that Unity has pretty good capabilities for building for different platforms so I might try build this as a mobile app at some point.
I noticed the problem with the leader board myself too. It seems that it works if it's opened before playing the game, but then afterwards it cannot be opened without crashing the game. I wasn't able to fix it before jam was over. I still don't know what is the issue but I'm pretty sure that there is something wrong with my LootLocker code.