The problem is back.
lsof -i :8443 | grep UDP
plugin-li 3573 mattermost 12u IPv4 27517 0t0 UDP *:8443
plugin-li 3573 mattermost 14u IPv4 27518 0t0 UDP *:8443
plugin-li 3573 mattermost 16u IPv4 26236 0t0 UDP *:8443
plugin-li 3573 mattermost 18u IPv4 26237 0t0 UDP *:8443
Should I kill the process and try again to enable the plugin?
edit: here is the process detail:
3573 ? Sl 0:22 \_ plugins/com.mattermost.calls/server/dist/plugin-linux-amd64