Big credit to: @Gwynevere and @Astonishing (192.168.1.2 and .astonishing on Discord):
(this applies for both mobile and emulator users)
It appears that by opening exchanges and the shop in general, the game gets gradually slower and slower even if you restart the game fresh. Like the "NEW" label and red dot notifications, meaning "you have not open this exchange yet", when you do open it to clear the dot if you're OCD like me, it will permanently slow down your game.
You can see the difference in these two videos: first video with NO exchanges opened / red dot notifications cleared; and second video after ALL of the exchanges were opened / red dot notifications cleared. The difference is MASSIVE!
Mind you, opening a few will not affect performance too much, so it's not like you shouldn't ever open exchanges, how else are you going to get your weekly pearl and stuff. There are exchanges that are lighter than others, and some super heavy, like the big list of awakening stone costumes (all of the game 4* costumes in the list).
This is to make the game fresh as new, super buttery smooth, and it avoids you having to download all game data and assets as if it were a clean (re)install (9gb or something from the force "Download" all data).
Gwyn found out a way to reset this choppiness, and it goes like this:
- Make sure your nier rein account is linked to the Square Bridge account (very important). DO NOT rely on facebook login, because it's down 99% of the time, not just for Nier, but as a whole. If you are only linked to facebook, DO link to Square Bridge account before proceeding.
- fully close the game (swipe it away from recents / force close, don't just put it in the background. otherwise if you just go back to main menu and proceed, it will not properly clear the flags needed to perform this cleanup).
- Open up the game, in the menu that says "press to continue", tap on the top right corner button, select Delete data (it does not reset your account, don't worry. the warning is about you having to have linked your account to the bridge so that you can log back in to your acc).
- It will restart and back to main menu, again press the top right corner, now tap Transfer data, login to your Square Bridge account to link the app to your account again.
- Done! your game is all new and silky smooth.
(You will have your client settings reset, such as the way you have set your characters / weapons sorted, etc. very minor things, a super small compromise for smooth performance and high FPS.)