[Samba] Best way to get to bottom of odd failures?

[frank picabia]

I have a Debian 11.3, all up to date, running Samba to provide shares.
It authenticates against Windows AD using security=ADS
smbd -V reports 4.13.13-Debian

The problems with our shares vary.

With one user, mounting the share to their Windows system
produces segfaults on smbd.  They can do small
transfers, but larger ones, say over 200MB, would fail.
It seems those transfer failures align with segfaults on smbd.

I see emails from root with tread debugging info for segfaults in smbd.

With myself, the mount works better.  I can transfer the Debian ISO
back and forth over it.  However, the progress meter goes to 100%
then says "an unspecified network error has occurred".  If I click Try Again
the transfer is redone, the file is over written and the second attempt is
perfect.

If I use smbclient on another Linux system, I see no errors at all.

I'm thinking, if I submitted a bug report, this isn't going to be
reproducible.
Also in many bug reports, people pick apart the config file and
say there was something wrong with it.  So maybe I should begin there?

The system in question was upgraded from Debian 9 to 10 to 11 and we
had no issues with the older versions, while using a similar configuration.

Here is what we have from testparam output.  I have replaced our domain name
as "example" or "EXAMPLE".

Load smb config files from /etc/samba/smb.conf
Loaded services file OK.
Weak crypto is allowed
Server role: ROLE_DOMAIN_MEMBER

Press enter to see a dump of your service definitions

# Global parameters
[global]
        bind interfaces only = Yes
        disable spoolss = Yes
        dns proxy = No
        interfaces = eth0
        load printers = No
        local master = No
        log file = /var/log/samba/%m.log
        max log size = 100
        nt pipe support = No
        obey pam restrictions = Yes
        panic action = /usr/share/samba/panic-action %d
        preferred master = No
        printcap name = /dev/null
        realm = AD.EXAMPLE.NET
        security = ADS
        server string = %h server
        template shell = /bin/bash
        winbind enum groups = Yes
        winbind enum users = Yes
        winbind refresh tickets = Yes
        winbind use default domain = Yes
        workgroup = EXAMPLE
        idmap config * : range = 69998-69999
        idmap config example : range = 70000-9999999999
        idmap config example : backend = rid
        idmap config * : backend = tdb
        force create mode = 0744
        force directory mode = 0755
        hosts allow = 111.222.
        nt acl support = No


[series]
        force group = www
        force user = www
        path = /usr/local/series
        read only = No
        valid users = teddy dave ronald


[cms]
        force group = www
        force user = teddy
        path = /usr/local/www/cms
        read only = No
        valid users = EXAMPLE\teddy EXAMPLE\ronald