The following change resolved the issue by starting SIP after DHCP has been initialised:
Old
New:
Thanks for the suggestion.
Old
Code:
[Unit]
Description=SIP for Python3
After=syslog.target network.target
New:
Code:
[Unit]
Description=SIP for Python3
After=syslog.target network-online.target
Wants=network-online.target
Thanks for the suggestion.