SOLVED SMB slow navigation after Windows upgrade

[PAE]

Greetings.
Recently, I switched from using LTSC branch of Windows 10 to consumer Pro (ver 2004, build 19041.508) and started having issues with samba performance. It became slow at listing folders containing any number of files. And the more files there is the slower it gets.
Eg. dir containing 159 files just took 29 sec to load.
I still have LTSC installation (ver 1809, build 17763.1457) available in dual-boot and it is not affected. All shares perform flawlessly and same folder lists instantly. May be same is true for non-LTSC branch of the same version, idk.
I have tried searching before posting, but things I tried (like "ea support = no", "store dos attributes = no") had no affect, and given that it works as expected in older Win, I figured that it is worth asking more experienced folks before messing with configuration.

Show : smb4_share.conf (options for share used to test)

Code:

        read only = no
        access based share enum = yes
        strict locking = yes
        level2 oplocks = no
        oplocks = no
        vfs objects = streams_xattr zfs_space zfsacl
        nfs4:chown = true
        nfs4:acedup = merge
        aio write size = 0
        mangled names = illegal
        ea support = false

Show : smb4.conf

Code:

[global]
        dns proxy = No
        aio max threads = 2
        max log size = 51200
        allocation roundup size = 0
        load printers = No
        printing = bsd
        disable spoolss = Yes
        dos filemode = Yes
        kernel change notify = No
        directory name cache size = 0
        nsupdate command = /usr/local/bin/samba-nsupdate -g
        unix charset = UTF-8
        log level = 1
        obey pam restrictions = False
        enable web service discovery = True
        username map = /usr/local/etc/smbusername.map
        username map cache time = 60
        logging = file
        server min protocol = SMB2_02
        unix extensions = No
        restrict anonymous = 2
        server string = NAS Server
        interfaces = 127.0.0.1 10.2.0.2
        bind interfaces only = Yes
        netbios name = nas
        netbios aliases =
        server role = standalone
        workgroup = WORKGROUP
        idmap config *: backend = tdb
        idmap config *: range = 90000001-100000000

        include = /usr/local/etc/smb4_share.conf

Datasets have "primarycache=metadata" set.
FreeNAS-11.3-U5 18GB RAM

Could someone, please, point me some directions to troubleshoot?

 

[PAE]

This is really confusing.
I tried creating new dataset from scratch, new share, checked ACL, tried messing with networking on the host..
On client side I messed with SMB signing, caching, NetBIOS settings, tried accessing both via alias and IP, tried PCIe NIC, turned off any checksumming options possible, turned off antiviruses. Nothing matters.

See for yourself short videos from LTSC and from Pro.

The thing I noticed is relatively large downloads on NIC corresponding to Pro version struggle with enumeration while there is nothing alike on LTSC.
And it seems that issue is not with the amount of files but rather with their size. Notice how my Plex media dir shows lower speeds during download activity on NIC, while there is twice as less files as in Photos folder. Even 2-4 10GB media files in other locations cause lag while navigating shares.

 

[PAE]

Windows does not stop to amaze.
First, I tested same shares in a second install of the same 'winver', that I already conveniently have had, and than accessing via Total Commander on main OS instance and it turned out to be issue of Explorer app. On problematic system I created new local user and found out it was not affected.

Repairing using "sfc /scannow" even after "dism.exe" against known good Win folder found some corrupt files, but not fixed issue at question.
So I had to switch to local account, add new admin user to del my existing user, recreate it and then sign-in to MS account again (all to maintain existing account directory path as I use scripting & symlinking for my configs).

So in other words, this time I got system files corrupt on fresh install even before I finished configuring my environment.. That's got to be a record of sorts.