My personal workaround to the start-up issues
If anyone is still struggling with the start-up issues, I tried around a bit with it and found a workaround that's been going well for me for the past days.
The start-up issue only happens on the first time you open the game after each reset (at least for me), but one thing that has been guaranteed to fix it for me was to open the game and disconnect my phone from the Internet shortly after the blue loading screen comes on. Upon getting the error message from that, I reconnect it, wait a few seconds and then press ok.
This has caused the game to boot up normally for me every time. If you press ok too quickly after reconnecting your phone or your Internet connection drops in that second, you may get sent back to the boot-up, so that's the only thing that could go wrong.
Otherwise, I hope this helps someone.