Proximity sensor causing problems to Knock Code

Two months ago I updated the firmware of my LG G2 D802 to Android 5.0.2 via the LG PC suite. After the installation I made a factory data reset to have a "clean" firmware.

Software info.
Kernel version: 3.4.0
Build number: LRX22G
Software version: V30b-EUR-XX

Currently this is the latest stock firmware.

I use the Knock Code as lock screen. The proximity sensor is causing a problem to the Knock Code after the update to Android 5.0.2.
It makes the smartphone believe that there have been 5 attempts to enter the code even if the screen hasn't been touched.
I've uploaded a video about the issue on YouTube.
Please search for "LG G2 D802 proximity sensor problem with Knock Code " because, as a new user, I'm not allowed to insert links.

It usually happens that the Knock Code recovery procedure is activated when I put the smartphone into my pockets.
The proximity sensor is working fine while phoning. I wonder if this could be a bug of the new firmware.

I installed the app Terminal Emulator. Is there a command to log the system related messages, something like the Linux terminal command tail -f /var/log/messages ?
In this way I could post the log and maybe a skilled user could help me to understand if it is a software or hardware problem.

Thanks for any help!

Bye!