For the sake of convenience, I’ve applied patches that skip everything before the title screen when booting the rom. However, the title screen is now completely broken, and uninstalling those patches does not fix the problem.
If the save data format is different, FE8U may behave in such a way.
For example, when you install EMS (SkillSystems), the save data format will be changed and you will see such a screen the first time.
The solution is to erase all save slots and create a new save data, or erase the sav file and restart game again.
This phenomenon is not seen in FE8J, so I believe it is unique to FE8U.