Thread:SunSlayerKD/@comment-31964100-20170509150834/@comment-30827145-20170510164043

According to the wiki, those islands should give the 5 gems rewards (can't remember, too long ago for me too). I guess finishing another island and paying attention to the number of gems before finishing the last stage would make things clearer if there is a bug or not with your phone. If it is indeed a bug, you should contact the support. I would try somewhere here:

http://bnfaq.channel.or.jp/contact