Sorry. Once I saw the 172.17.x.x addresses I assumed that you had a reverse proxy.
So this is a standard install?
If you’ve got a single host and no load balancer/reverse proxy, then I don’t know how anyone would have such an IP address. Maybe something else is somehow forwarding traffic? Those are private addresses, so it would appear that they are coming from your local network. That suggests that the spam bot is living on your network. (Guide to Private IP Address Classes and Ranges - Ipstack)
If you don’t have legitimate users (e.g., people on your LAN) accessing Discourse from that IP range, you’re safe to block it. I’d contact someone who runs your network and let them know that these attacks are coming from those internal addresses..