>reads thread title
>mac
ugh i dont know about anything about that os
anyways ill try my best
https://play.google.com/store/apps/details?id=com.estrongs.android.pop&hl=de
download this (with an apk downloader, im assuming you know how that works)
run the app on bluestacks
go to root (click on the / in the navigation bar)
click on the folder called data
click on the folder called data in that folder
now you should see all folders with your appdata. tap one then tap ... select copy and paste it somewhere save.
that's how you do a backup.
after that, uninstall bluestacks and reinstall it.
after that, redownload the app you want
dont open it
copy and paste your folder you backed up back into its original location
Source: http://android.stackexchange.com/questions/102377/where-are-the-game-save-files-located-in-pc-bluestack-question
A clean install is always the first thing you should try if you get weird errors imo.
E: wait that might not work if it happens as soon as bluestacks is starting
you could try navigating to that folder by yourself, although i know nothing about osx system architecture so i couldnt tell you where to look for bluestack's files.
FYI theres a folder called "ProgramData" (its not visible by default) on windows where bluestacks saves data in.