I never used Kingoroot, so can't be sure if it provides and option for master mount (
su mm) or not. You can switch to Magisk or SuperSU once the device is rooted. If you can't or don't want to, you can use:
su -c 'nsenter -t 1 -m /system/bin/sh'
from commandline instead of simple
su. This will make you switch to root mount namespace. For details see this answer.
nsenter is usually available as busybox applet.
Since mount namesapce was implemented in Android 6, this might not be the problem with your KK device.
If Kingoroot works for you, it indicates that your device has some serious security flaw(s). Do consider an upgrade.