Logcat not working on my LG G4 (H815)
Are you using a custom rom ?
I have the same problem, here is how I solved it partially:
Download this:
https://drive.google.com/file/d/0B7Mx2p0Jd24Jcm9fNEV6d0xDV1E/view

Put this file to root/system/bin an rename it to logd. Attribut -rwxr-xr-x (755) an reboot your Phone. After that logging works.
This file has been deleted because it consumes a lot of battery.
After logging, rename the file in logd.xxx and restart your phone. Thereafter, the battery consumption is reduced again.

More Description
http://forum.xda-developers.com/g4/help/guide-disable-logd-process-battery-drain-t3308921#post65168793

then download a logcat reader app from playstore.
Unfortunately, logcat from computer still don't work :( I'm still searching a solution for logcat from computer