Never head of this option before, but that was the trick. Adding the –ws-port=8081 in deconz.service did the trick. Both webinterfaces come online, and both work without issues for now.
[Unit]
Description=deCONZ: ZigBee gateway – REST API
Wants=deconz-init.service deconz-update.service
StartLimitIntervalSec=0
[Service]
User=1000
ExecStart=/usr/bin/deCONZ -platform minimal --http-port=8081 –ws-port=8081
Restart=on-failure
RestartSec=30
AmbientCapabilities=CAP_NET_BIND_SERVICE CAP_KILL CAP_SYS_BOOT CAP_SYS_TIME
[Install]
WantedBy=multi-user.target