Yes it doesn't have item in the BD2 obb folders, we same.
Jus try step follow :
1 - Install the BD2 (Original) from apk or play store.
2 - Open the BD2 (don't download full data) then try goto login into google account email then exit the BD2 app.
3 - Open the file manager then try goto find the folders:
internalstorage>android>obb>com.neowizgames.game.browndust2x (rename add "x" in the folders full name BD2 obb)
4 - Uninstall the BD2 (Original) and go to open file manager then Goto find the folders:
internalstorage>android>obb>com.neowizgames.game.browndust2 (rename remove the "x" in the folders BD2 obb)
5 - Install the BD2 (Signed mod apk) then Open the BD2 (Signed mod apk) then try goto login into Google account email as same before you choose one) done!
If still can't login, it keep says failed login then can't help
sorry.
The guy said "The second method u can learn from this website they teach how to deal with the obb file."
Ps they made it works that I sent PM em.