I wanted to post a follow up with the issue and solution (after a few rounds of back and forth with TP Link's R&D)! If you have too large an IP range in the "IP Address" list then "Access Control"...

@JoeSea ER605 WAN does not have IPv6 enabled and the LAN device I'm trying to filter is IPv4 assigned IP only connected to an IPv4 server. There's no IPv6 assigned or in use on the device I'm trying...

@somnus Thanks for the reply - I forgot to put that I already tried "ALL" for the service type for both directions. That doesn't work either (and I did reboot the router to see if that helps, it...

TLDR: No matter what "Access Control" policies I set, they do nothing. I can't find any option to "enable" the Access Control as a feature so I'm left to assume that Access Control is busted. Quick...