Failed to see all Directories in Admin page and in GUI at user end

Ok.  So shares that were present in web ui before are no longer shown, but the data is still intact when you look with ssh?

If so, I think the first thing to check is that the OS partition has a good amount of free space.  A full (or nearly full) OS partition can cause a lot of problems, and one of them is corruption of the NAS configuration files.  You can do that with the btrfs fi show command

root@NAS:/# btrfs fi show //
Label: '2fe72582:root'  uuid: b9eb2386-9157-4946-8233-bd275c82a515
        Total devices 1 FS bytes used 998.05MiB
        devid    1 size 4.00GiB used 1.53GiB path /dev/md0

As you can see, it is nomally about 25% full  (998.05 MiB of FS bytes).

The total used (in the last line) is also relevant - that includes space that is allocated, but not actually used for files.  As you can see, in my own system the allocated space is about 38% of the total.

If your space usage is substantially higher than my numbers, you should post back.  Apps will make some difference in this (though apps are supposed to use the data volume /.apps folder for storage, some don't do that).

If the OS partition looks good, then there is an ssh repair script you could try: https://gitlab.codycook.us/readynas-scripts/share_lun_ui_fix.sh

This script was written by someone at Netgear - but like all ssh usage, you are on your own if you try it.  It would be wise to make sure you have a backup of your files before you run it.  Still, others here have used it successfully, and I haven't seen a report of it doing damage.

Another thing you could do for each missing share:

1. rename the missing share with ssh
2. create a new share with the original name
3. destroy the new share (empty) with ssh using btrfs subvol delete
4. change the name of the original share back to the original name.

This won't work for missing home folders, but it should work for ordinary shares.