The random wallpaper selection feature tries to load "dot underscore" metadata files generated by macOS, and then defaults back to the checkerboard image

[parkamonster]

On macOS, if you populate the wallpapers folder with a bunch of images, an equal number of dot underscore files will be generated due to the destination volume being a non-Apple file system.

For example, copy these files across…

Wallpaper1.png
Cool Picture.jpg
Background 4.jpg

…and macOS will detect that the files are going to a non-Apple file system and generate metadata these files along side them…

._Wallpaper1.png
._Cool Picture.jpg
._Background 4.jpg

Unfortunately, the random wallpaper selection feature will include these metadata files in its list of images, meaning that literally half of the files will fail to load, reverting back to the checkerboard image. Delete these metadata files and you never see the problem again!

MiSTer should filter out these files, which are impossible to delete without a trip to the Terminal, or the installation of paid 3rd party utilities to clean the drive of Mac metadata (such as BlueHarvest, $12.99).

[limi]

Irrespective of macOS’ bad behavior here, MiSTer’s wallpaper loading code shouldn’t enumerate and attempt to load files that are hidden in Linux either. Any file starting with a dot should be ignored.

[ojaksch]

Good point! MiSTer's /etc/samba/smb.conf could include a line
hide files = /.*/
per default and per share and problem would be gone...

[sorgelig]

i've added commit skipping dot files. Try latest unstable build.