Poor Samba performance after upgrade to IPA 4.6.5/Samba 4.9.1

Hi,

this may be something obvious, but i need a hint in the right direction:

I recently upgraded to IPA 4.6.5/Samba 4.9.1 via regular CentOS update. Samba
runs on IPA server.

Samba shares are still working, but there is a performance decrease of about an
order of magnitude (~4-5 MB/s vs. 40-50 MB/s before).

Any ideas?

Mit freundlichen Gruessen/With best regards,

--Daniel.

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/etc/redhat-release:
---
CentOS Linux release 7.7.1908 (Core)
---
$(rpm -qa | grep '^ipa\|^sss\|^samba' | sort):
---
ipa-client-4.6.5-11.el7.centos.3.x86_64
ipa-client-common-4.6.5-11.el7.centos.3.noarch
ipa-common-4.6.5-11.el7.centos.3.noarch
ipa-server-4.6.5-11.el7.centos.3.x86_64
ipa-server-common-4.6.5-11.el7.centos.3.noarch
ipa-server-trust-ad-4.6.5-11.el7.centos.3.x86_64
samba-4.9.1-10.el7_7.x86_64
samba-client-4.9.1-10.el7_7.x86_64
samba-client-libs-4.9.1-10.el7_7.x86_64
samba-common-4.9.1-10.el7_7.noarch
samba-common-libs-4.9.1-10.el7_7.x86_64
samba-common-tools-4.9.1-10.el7_7.x86_64
samba-libs-4.9.1-10.el7_7.x86_64
samba-python-4.9.1-10.el7_7.x86_64
samba-winbind-4.9.1-10.el7_7.x86_64
samba-winbind-modules-4.9.1-10.el7_7.x86_64
sssd-1.16.4-21.el7_7.1.x86_64
sssd-ad-1.16.4-21.el7_7.1.x86_64
sssd-client-1.16.4-21.el7_7.1.x86_64
sssd-common-1.16.4-21.el7_7.1.x86_64
sssd-common-pac-1.16.4-21.el7_7.1.x86_64
sssd-dbus-1.16.4-21.el7_7.1.x86_64
sssd-ipa-1.16.4-21.el7_7.1.x86_64
sssd-krb5-1.16.4-21.el7_7.1.x86_64
sssd-krb5-common-1.16.4-21.el7_7.1.x86_64
sssd-ldap-1.16.4-21.el7_7.1.x86_64
sssd-libwbclient-1.16.4-21.el7_7.1.x86_64
sssd-proxy-1.16.4-21.el7_7.1.x86_64
---
/etc/samba/smb.conf:
---
[global]
create krb5 conf = No
debug pid = Yes
dedicated keytab file = FILE:/etc/samba/samba.keytab
domain master = Yes
interfaces = eno1
kerberos method = dedicated keytab
ldap admin dn = cn=Directory Manager
ldap group suffix = cn=groups,cn=accounts
ldap machine suffix = cn=computers,cn=accounts
ldap ssl = no
ldap suffix = dc=example,dc=com
ldap user suffix = cn=users,cn=accounts
map to guest = Bad User
log level = 0
max log size = 90
passdb backend = ipasam:ldap://ipa.example.com ldap://ipa.example.com
realm = EXAMPLE.COM
registry shares = Yes
security = USER
server min protocol = SMB2
winbind enum groups = Yes
winbind enum users = Yes
workgroup = DIGI
ldapsam:trusted = yes
rpc_server:epmapper = external
rpc_server:lsarpc = external
rpc_server:lsass = external
rpc_server:lsasd = external
rpc_server:samr = external
rpc_server:netlogon = external
rpc_server:tcpip = yes
rpc_daemon:epmd = fork
rpc_daemon:lsasd = fork
idmap config * : backend = tdb
cups options = raw
hosts allow = 127. [...EXAMPLE.COM IP SUBNET...]
use sendfile = Yes

[homes]
browseable = No
comment = Home Directories
inherit acls = Yes
read only = No
valid users = %S %D%w%S

[...]

[HiWis]
comment = HiWis
force create mode = 0664
force directory mode = 0775
force group = dtstud
path = /home/pubsamba/HiWis
read only = No
write list = @exstud @ex
---