Scenario, my router, AX1800 v1.2, is connected to my ISP modem to provide WIFI and LAN connectivity to my devices.

The problem is when using any form of mutlicast from WiFi devices, i.e. any device connected via WIFI cannot using mutlicast, which means technology like casting and upnp for automatic opening of ports do not work at all. Any device connected directly to a LAN port on the ISP modem or TP-Link router immediately picks up my wired TV as well as able to use UPNP to open ports automatically on my ISP modem. No form of bridging is used, i just disabled DHCP on the TPLink so my ISP router can give LAN addresses. 

I have tried Wireless AP and Router mode to no avail.

Has anyone experienced this? Is there any workaround or fimrware fix?

Not being able to cast from my WIFI connected laptop to my wired SmartTV is a pain, the neighbour who lives 200ft away who I allow to use my WIFI TV immediately comes up when i open the cast menu on my laptop or phone, put simply casting works from WIFI to WIFI devices and between LAN devices but not between LAN to WIFI.

Is this router a firewalll???  Plz fix TPLINK, my old router did this without issue :/.