EXT4 Mount gives this error "SELinux: mount invalid. Same superblock, different security settings"

Question

I am trying to mount a second partition (ext4 ) for my apps ( I guess its a bit outdated with adoptable storage but then ext4 isn't accepted FS for adoption for external card ) . I am on 9.0 ( Pie ) and all my SD partitions are mounted under /storage and some weird name .e.g.

/storage/ 6226b27a-ebc1-4fdd-b54c-096abc40c2b9

Now I need my 2nd Partition to be mounted under /data/sdext2 but O.S already mounts it. app2sd ( link2sd) gives me Mount script argument invalid argument . No matter what .

On digging further through OS logs I get this info

[   48.820728] EXT4-fs (mmcblk1p2): mounted filesystem with ordered data mode. Opts: nomblk_io_submit,errors=remount-ro
[   48.941276] EXT4-fs (mmcblk1p2): mounted filesystem with ordered data mode. Opts:
[   48.969786] sdcardfs: mounted on top of /mnt/media_rw/6226b27a-ebc1-4fdd-b54c-096abc40c2b9 type ext4
[   48.970918] Remount options were mask=18,gid=9997 for vfsmnt ffffffda2f7539e0.
[   48.971668] Remount options were mask=18,gid=9997 for vfsmnt ffffffda95617660.

......

[  107.476736] SELinux: mount invalid.  Same superblock, different security settings for (dev mmcblk1p2, type ext4)

What I did :
Umount partition as mount master under Terminal Emulator. Its umounted only in context but not everywhere. But in-spite of umount I cant seem to mount it under /data/sdext2

Whats happening and how to work around .
On a side note. How do I manually assign mount point names and prevent these weird names given by OS to the partitions and on a 'side side' note. I am not even sure if this is the reason for invalid mount error as I read elsewhere its more of a benign FYI message.