This is something that was quickly broached when the Samsung One Ui was released.
It maybe due to the fact that the Night Mode is a system wide change and Samsung does not control the themes directly made by the developers of the themes that are uploaded to the Samsung Theme Store.
Probably clashing issues.
Current Phone ~
Samsung Note 20 Ultra 5G SM-9820 _256Gb SnapDragon 865+
Samsung One Ui 2.5/ Android 10.