In addition to all of the suggestions here you can easily do this with almost all major DNS providers today like Cloudflare and AWS Route 53, there are many community containers and scripts to keep the record in sync depending on what else you are using on your network.
Your netstat command shows a process named docker-proxy using that port, which confirms what the log says. If your container isn’t running you can try to find the process using it with netstat or lsof, it might be a stale container process or something but a reboot is often faster than figuring out what it is to see if that clears up whatever is using the port.