I accepted the free blue cub reward given, but when i looked through all my Arkadions like 10 ten times, it was not there. I tried to claim it again, but it said reward has already been claimed. I don’t know if it is a bug or something.
It is a bug. However that monster is only available once per device so you can’t get Blue Cub on any other save files. If you aren’t far in the game your best bet is do reinstall the app (Free of course). Then you should be able to get Blue Cub again. Sorry for the inconvenience.