Metafiles / BR Cover for MKV files

Hi,

I am currently doing some tests with Serviio and until now, I really like this programm and appreciate your work
To make life easier, let's call BluRays "BR"

I am only struggeling with one part: I've activated the automatic Meta - Information Research (not sure if it is called exactly this way in english).
My Files are all within one folder, I did not seperate them in any way.
The filename for common BRs is just the name of the movie, like <name>.mkv
The filename for 3D BRs is the name of the movie and a 3D prefix, like 3D - <name>.mkv

The Meta Information Research works pretty fine for most of my BR and 3D BRs, round about 80%.
But some movies do not get a cover when I look on my TV for any reason.

I already tried to add the year to the file name like 3D - <name> (2015).mkv but this didn't help at all.

My next try was to download a JPG file, call it dvdcover.jpg
Then I used MKVtoolnix, went to "Attachments", right clicked in the lower box and attached this JPG file.
Then I muxed it (Love this word...)

But unfortunately this does not change anything, the movie still got no cover on my TV.
What went wrong, how can I handle this?

I had a closer look into the file after MKVToolnix added the cover.jpg

The tool worked fine, the cover file is in there.

But for any reason serviio denies to show the cover.

After changing to the strict name convention <<Name>> (<<Year>>).mkv it is working fine now.
Unfortunately I've lost my "3D - ..." prefix now

Any idea how I can get both, covers AND an 3D marker?