From what you've described, it sounds like the Pi agent likely installed OK and just isn't connecting to our Cloud Server after the Pi reboot.
It sounds like you may be on to something with regard to the public wifi -- the Cayenne Raspberry Pi agent needs port 8181 to be open in order to connect to our cloud server. If you have access, even temporarily, to put the Pi on a network where you can confirm that is open, that would be a good test. This post has great troubleshooting steps on getting the Pi to connect to our cloud server that you can walk through as well. It also has steps to confirm if your network has port 8181 open.
It is of course possible that our install failed for some reason. The reason I asked (and still want to know) whether you installed via the mobile app or via our web dashboard, is because in the former case, there is not much error messaging displayed in the mobile app. It sounds like you probably installed via mobile?
If you did install via mobile, and the above troubleshooting steps didn't resolve the issue, the next best move is to install via command line from the web dashboard.
To do that, first run these commands to uninstall anything which may have been left behind from a failed installation:
Next, log into your account and do Add New > Device/Widget > Single Board Computers > Raspberry Pi and scroll down to Option 2. Install from those commands on the Pi itself, rather than from the mobile app. It does the exact same thing as the mobile app, but because you're at the command line, you'll be able to see any relevant errors displayed if and when the install process fails again, and be able to share them here. Here is hoping that it was just your network and you never have to go this far!