Ubuntu-based CUPS server gets progressively slower after reboot; Windows XP clients connecting to server

Question

I have 2 Windows XP clients running lab equipment. These are Samba version 4.7.6 clients of Ubuntu 18.94.2 (64 bit) server running CUPS Ver 2.2.7 all has been working for some years and the only changes are updates to Ubuntu and CUPS. To allow Windows XP clients I have set smb.conf as shown below: I have noticed that the printer hangs and/or take hours to print.

After a reboot, initially works OK but gets slower and slower as though a buffer is filling up or a similar bottleneck? Looking at the CUPS error log I see these lines below appearing.

The server and two Windows XP workstations are not connected to the Internet as they just run our own code in a local environment.

Can anyone thrown me a lifeline?

CUPS error log:

E [10/May/2019:16:19:09 +0000] [Client 2] Unable to encrypt connection: A TLS fatal alert has been received. 
E [10/May/2019:16:19:30 +0000] [Client 8] Unable to encrypt connection: A TLS fatal alert has been received. 
E [10/May/2019:16:19:57 +0000] [Client 23] Unable to encrypt connection: A TLS fatal alert has been received.
E [10/May/2019:16:19:57 +0000] [cups-deviced] PID 8878 (gutenprint52+usb) stopped with status 1! 
E [10/May/2019:16:19:59 +0000] [Client 29] Unable to encrypt connection: A TLS fatal alert has been received.

SAMBA config:

Global parameters

[global]
add group script = /usr/sbin/addgroup --force-badname %g
add machine script = /usr/sbin/useradd -g machines -c "%u machine account" -d /var/lib/samba -s /bin/false %u
add user script = /usr/sbin/adduser --quiet --disabled-password --gecos "" %u
bind interfaces only = Yes
client max protocol = SMB2
dns proxy = No
domain logons = Yes
interfaces = 127.0.0.0/8 enp0s25
lanman auth = Yes
log file = /var/log/samba/log.%m
logon drive = H:
logon path = \%N\profiles\%U
logon script = %U.bat
map to guest = Bad User
max log size = 1000
ntlm auth = ntlmv1-permitted
os level = 64
pam password change = Yes
panic action = /usr/share/samba/panic-action %d
passwd chat = Enter\snew\s\spassword:* %n\n Retype\snew\s\spassword:* %n\n password\supdated\ssuccessfully .
passwd program = /usr/bin/passwd %u
security = USER
server role = classic primary domain controller
server string = %h
template shell = /bin/bash
unix password sync = Yes
usershare allow guests = Yes
wins support = Yes
workgroup = XXXXX3.LOCAL
rpc_daemon:spoolssd = fork
rpc_server:spoolss = external
idmap config * : backend = tdb

[homes]
browseable = No
comment = Home Directories
create mask = 0775
directory mask = 0775
read only = No
valid users = %S

[netlogon]
comment = Network Logon Service
guest ok = Yes
path = /srv/samba/netlogon

[profiles]
browseable = No
comment = Users profiles
create mask = 0600
directory mask = 0700
path = /srv/samba/profiles
read only = No

[printers]
browseable = No
comment = All Printers
create mask = 0700
guest ok = Yes
path = /var/spool/samba/
printable = Yes
use client driver = Yes
write list = @users

[print$]
comment = Printer Drivers
path = /var/lib/samba/printers
write list = @lpadmi