I was using my MK808B+ with 2011, 2012 and 2013 models with no issues. Please try using a different HDMI cable. It is also possible that your MK808B+ is a bit faulty.
Unfortunately there is no point in grabbing logs, I did a pretty intensive CEC debugging session back in 2016 and in current state it's the best what I can get.
Please also look at the first post: I am not working on these builds any more (lack of time). The only update S805 devices will get is a bump to Kodi Leia (soonish)
Any idea on when the new version for Leia will be release.
Thanks again for your work kszaq!