My guess is one of the Magisk mods that folks are using is not playing will with a custom kernel. The thread by @Freak07
has some reports also. Over there it is seemingly good to go with a stock setup other than the kernel. I'm sure once enough users get involved with a wider pool of variables, it'll become obvious what is causing this behavior. I'm personally experiencing it once in a while but as you said a hard boot fixed it. I also almost always have to reboot a second time after adding or updating a magisk module.