Ok, I've found the solution myself, leaving it here for future seekers.
I had to comment the following line in file /usr/lib/systemd/system/cloud-final.service:
ExecStartPost=/usr/bin/systemctl reload-or-try-restart NetworkManager.service
Now my file looks like this:
[Unit]
Description=Execute cloud user/final scripts
After=network-online.target cloud-config.service rc-local.service
Wants=network-online.target cloud-config.service
ConditionPathExists=!/etc/cloud/cloud-init.disabled
ConditionKernelCommandLine=!cloud-init=disabled
[Service]
Type=oneshot
ExecStart=/usr/bin/cloud-init modules --mode=final
RemainAfterExit=yes
TimeoutSec=0
KillMode=process
ExecStartPost=/bin/echo "try restart NetworkManager.service"
# TODO: try-reload-or-restart is available only on systemd >= 229
# ExecStartPost=/usr/bin/systemctl reload-or-try-restart NetworkManager.service
# Output needs to appear in instance console output
StandardOutput=journal+console
[Install]
WantedBy=cloud-init.target