Use Citrix Receiver (ICA client) on Ubuntu 18.04
Running the below commands after installing the Citrix Receiver Full worked for me
sudo ln -s /usr/share/ca-certificates/mozilla/* /opt/Citrix/ICAClient/keystore/cacerts/
sudo c_rehash /opt/Citrix/ICAClient/keystore/cacerts/
Looks like this is a known issue in older versions which comes back in 13.9. So nothing Ubuntu related. Only seams so because Citrix Receiver 13.9 and Ubuntu 18.4 was released in the same period of time.
@Rinzwind, got this insight from your link here: https://discussions.citrix.com/topic/323985-cannot-connect-to-0002-published-app-name-most-distros/#comment-2004606
So to resolve install Citrix Receiver 13.8
I had this problem after upgrading to 18.04 from 17.04. Firefox gave the same error message. I found a work-around: Start Citrix Receiver directly from the Launcher (Supe+A). Enter a copy from the url you can still find on the Firefox page.
Btw: Still using citrix Receiver 13.5