If you find some free time, pls do check it out. as weird as it may seem, that app will only detect root on Ketan Rom, I don't know if you remember me but we tried working on the Note 8 OEM Unlock fiasco before haha, anyways will try and check back once the rom gets updated again. thanksI have no reason to believe it's a rom issue. It's all about magisk, your existing setup.
I have nothing to offer, you can switch rom if you find it working on other rom.