Enable Logcat in CM12 NIGHTLY Galaxy S4 jftlexx

Hi everyone! I'm trying to develop an app with Android Studio but whenever I try to check the logcat logs, nothing appears.

I have a Samsung Galaxy s4 with CyanogenMod Version 12.1-20150623-NIGHTLY-jfltexx installed. Android Studio is actually at version 1.3.2.

When I try to read app log messaes through Android Studio Device Monitor, I get the following error message:

DeviceMonitor: Adb rejected connection to client '11998': closed

When I try to manually launch Logcat from terminal using this command from the platform-tools directory:

adb logcat

I get the following error message:

Unable to open log device 'main'

I tried to find how to enable logging on my smartphone but I'm totally lost and I would really continue to develop my app.

Is anyone aware on how should I enable logging on my CM12?

Thank you so much in advance, I'm desperate

Diego