I am having a very similar issue described in this thread. https://community.tp-link.com/en/home/forum/topic/620334

My UN49KU7000F Samsung TV was able to connect to the 5GHz band of my ISP provided router without a problem. However I am unable to connect to the 5GHz band of my AX3000 Pro router unless I disable all security. I am able to connect to the 2.4GHz band with security enabled. I tried manually setting the IP address, subnet mask, and DNS using the values assigned when connected to 2.4GHz but those same setting do not allow me to connect to 5GHz.

This is the error message I get when I havn't manually set the IP settings.

Here is what I get when I have manually set the IP address