The title pretty much says it all. What does "mount namespace separation" in the app SuperSU do and how does it affect other apps?
From the man page for
A mount namespace is the set of filesystem mounts that are visible to a process.
It makes it so that the superuser has separate mount points visible to it from the rest of the system/apps. I believe the intention is to prevent any issues when remounting partitions, such as remounting
/system as read-write. With this option enabled it should remain read-only to unprivileged apps.
It can, however, just break things more. It made my SD card unusable in root apps: Internal and external SD storage inaccessible as root