I installed 1.8.0 yesterday and the first thing I tried was pinging the IP address assigned to the device I have on the 5GHz guest network with my wired computer. No response. However, today I tried pinging the same device again and I got a response. I had this issue with previous versions of gargoyle as well.
Client isolation is enabled on the regular and guest networks. I only have my TL-WDR4300 so I can't test other devices.