I can not reproduce it.
It is working properly.
If you are using an older version, please use the new version.
I will explain how to change battle animation.
In this example, I will put anime of Lyn in Eirika.
Open the ROM of FE7U.
Select Other editors.
Select battle animation.
Since it is animation of Lyn, select 0x0F animation.
And,Press the Export button to save.
Once you have exited the editor,
Newly, load FE8U.
Likewise, entering battle animation,
Since it is a battle animation of eirika, I select 0x03 animation.
And, From the Import button, let's load the Lyn animation saved earlier.
Please press the F5 key to launch the emulator and check the operation.
If this does not work,
There is something conflicting with existing remodeling of your ROM.
Please explain in detail the ups patch and the reproduction method to reproduce the problem.