@RicoHTPC using IE or Edge? They have a tendency to rename .mpe1 to .zip and if you choose to "open" when asked it will open the zip file (hence the files).
In 1.15 Pre and 1.15 Final the "Use MediaPortal volume controls to adjust HDMI audio systems volume" setting does not work. It did work for me on 1.13 Final.
Started with watchdog and empty log folder -> try to change volume with MCE remote -> exit MP.
One question (that I cant find answer to), how do I rebind the keys? Im trying inside MP config - Plugin and CEC plugin, key mappings but I cant get it to work. Trying to bind RecordedTV to red button.
After contacting Pulse-Eight support it turns out the issue was with the Pulse-Eight provided short HDMI cable which was rated for HDMI 1.4b and does not work properly with HDMI 2.x.
Replacing it with a proper HDMI 2.x cable fixed my issues. The CEC adapter itself works great so far over HDMI 2.x too.