"Sorry to bother you with this since I just figured out the problem.
I had the devices on my guest wifi networks. I tried switching one over to my main network and it worked. I read somewhere you should keep smart home stuff on your guest network for security reasons, but I guess that doesn't work for Hubitat."
To build off of this. I have a separate VLan locked down from my main network with all of my IoT devices on it, the hubitat included. It basically drops all internal traffic as well and just allows access out to the internet when needed. To make this solution work, would I have to allow the hubitat accept pings to the IP of the TP-Link? Is there anyway to add via IP instead of discovery since we are assigning static IPs anyway? I didn't get a chance to mess around with it too much last night, but basically it was looking for devices for about 1-2 minutes and then found none, with nothing responding which isn't surprising based off my firewall rules.
I just wanted to get your thoughts, I Think a rule as mentioned above should allow it to see the device and that is fine. I could see others running into this in the future, having IoT things locked down is definitely a good way to go on a home network.