Hi @rgrz,
I split your question into a different topic because even though you get a similar error it is probably caused by something else, since you are using --nginx mode and not --standalone mode.
I suspect in your case you just have a different service enabled that is also taking up port 80. Since you already killed it, it’s impossible to tell what it was. If it happens again, you could run fuser without the -k option to identify the process ID numbers without killing them and then run pgrep with those process ID numbers to identify what program is holding the port.
In the meantime, if you share the output of systemctl list-unit-files it might reveal a conflicting service.