Problems with HDMI-CEC after software update on my LG C3

I've bought a 77" LG C3 a couple months back and use it with a Denon S670H AVR. The setup worked perfectly, I have a Nvidia Shield TV used for Plex connected to the AVR aswell as a Blu-ray player. The AVR itself is connected to the TV via the eARC HDMI port.

Now a couple of days ago I updated the software on the TV to version 23.20.50 and since then, I got some very annoying problems with my speakers:

In about 80% of the times I press the Home button on the LG remote to go back to the WebOS homescreen, my AVR will change its sounds source to the latestly used HDMI connection (e.g. my Blu-Ray Player), even if the device itself isn't running. Since I'm using many different apps directly on the TV, this is pretty annyoing. I always have to change the sound source manually on the denon remote.

Have any of you guys experienced a similar behaviour? Or have you any tipps on how to resolve this?