When I logged in to the Omni Hotel WiFi in Nashville, TN, I received the following warning from my Nextcloud file share.
You see the ssl.elevenwireless.com? Yup, they are attempting to conduct deep packet inspection on my traffic. In short, what that means is that they are intercepting your traffic on the way out of their LAN, reading your traffic, and inserting a 3rd party certificate before it goes back out to the internet. this is called Deep Packet Inspection, or DPI.
The solution is to use a VPN, preferably one that you can you custom DNS.