Users' key is getting deactivated

Hi, we're using Lime LM for our software and had a couple of issues with users reporting that they activate the license and have to reactivate after a few days. All of them are usually disconnecting from the Internet after activation. To quote:

Today at Welcia, I had to input the licence again on the 4 devices. Since the devices are not connected to the Internet continuously, I guess this is the expected behavior.

Any knowledge on how we can prevent this?