Due to a recent Safari update, your Citrix application may need to be enabled within the preferences.
Safari will set it to "ask" in the permissions when Safari, MacOS or the receiver have been updated, which will cause the applications to not open automatically. Luckily these settings can be corrected fairly easily.
First, we'll navigate to apps.swizznet.com in Safari.
On the top menu of the Computer we'll click Safari > Preferences.
A new box will open and we'll want to make sure we're in the Security Tab.
On the bottom we'll see Internet Plugins.
We'll want to make sure "Allow Plugins" is checked and Click on "Plugin Settings".
A new Window will open with the different plugins and we'll choose the Citrix Receiver on the Left menu.
You'll see "Currently Open Websites" and see apps.swizznet.com on the right side of that window. We're going to change where it says ASK to ON.
Once complete, we'll click done and the app will launch.