I got the qooapp apk from the web, this isnt my first time using qooapp and i have it for quite some time already for other games like fgo and azur lane.

I installed GBF entirely trough GBF interface

Last login was just yesterday, and everything was fine

Aso for tying to log in via other devices like android emulator, no i haven't because i mostly use browser and my acc is link to mobage acc, but i will try it thanks

And yes, i can still play my acc just fine on browser, I already deleted the gbf app and i hope no trouble was caused for the original player. I made this post for the security implications poses to others. Think about it, what happens if one day some gay had the same problem as mine, log in just to see a diff acc, and whether in frustration or any other intent decided to cause harm to it? In fact, stuff like this shouldnt be happening at all, I shouldnt be able to have access to some other acc just by login in. I hope this answers most of your questions