WRT3200ACM 88W8887 Third Radio
DON'T EVEN THINK ABOUT TRYING TO ADD AN ADDITIONAL (aka VIRTUAL INTERFACE / "NEW INTERFACE") TO THE WRT3200ACM'S THIRD (model # 88W8887) RADIO!!!
It will not work, and you will totally hose the LuCI GUI (naturally, modifying wireless settings will affect a completely different service). This will require that one modifies the /etc/config/wireless file to remove any offending settings and then restart the router (because naturally, restarting the UHTTPD service does no good what so ever).
This applies to OpenWRT 19.07.03 (maybe they will / fixed it with some later version)