FAQ
On a fresh install (i.e. not updating an existing release) the magisk app does not show up first. A reboot is required to make it available.
After the reboot you will find the Magisk app in your app drawer but it does not have a logo and when starting asks for downloading Magisk files.
This is expected (and wanted) behavior. See "After I hidden the Magisk app, the app icon is broken" for details (it applies to this situation as well).
There was a workaround possible before but the app itself can't be integrated as a system app anymore (magisk contains a stupid check for that) and HAS TO be installed in /data - which is not available during the ROM build.
also check the next FAQ
previously tracked here.
After a fresh install (and also after an OTA including an updated magisk version) the startup of magisk shows an error:
Simply select OK here and let it reboot once. In some cases this message will re-appear somewhen which you can simply ignore then.
The reason for this is similar to the previous FAQ: during build time there is no way to identify a valid partition to place magisk files. Even if we use (e.g.) the fstab found it would become complicated to pre-init this for magisk. It is possible, yes but not worth it (imho) as this is a one-time-and-forget task.