Wow, a very nice answer very quickly -- impressive. Unfortunately neither of the two router layers this computer is behind has the capability to block incoming connections by remote IP, but definitely a reasonable suggestion. I do use RDP (very handy; sole reason to get Windows Professional over Home for me), so I don't want to close that port. I could change the port number, but that's only a temporary solution.
Is there a way to configure Malwarebytes to not pop up notifications for this kind of protection? It looks like adding this (malicious) IP to my "Allow" list would achieve the desired result (no pop-ups, still protected by Windows Firewall), but that feels a little dirty.
As an advanced feature request, is there any way a future version of Malwarebytes could check the Windows Firewall settings so as not to duplicate them?
I'm open to other suggestions to avoid this pop-up, but I suppose the current "best" solution appears to be to add the malicious IP to my Malwarebytes "Allow" list after adding a blacklisted Windows firewall entry. Second choice after that currently would probably be finding a different brand of protection software 😕