Sessions not working on php 7.1.3

Hello

I'm having a hard time getting CI sessions to work with one of my installs. My development machine has php 7.1 installed (windows) with the latest version of CI (3.1.3) and it runs just fine. However when I tried the same code on my Ubuntu machine (7.1.3-2) suddenly all my sessions just don't work anymore. No logs are made, even with the highest threshold. 

Is there a workaround for this or is CI not ready yet?