I'm having the same issue on PC (EGS Version). I have tried verifying files, uninstalling/reinstalling the game, and creating a new game to see if it was my save. I have tried it with multiple trucks on multiple maps and it always says "This trailer does not support this cargo".
On Xbox One version, new logging frame addon for trucks does not accept logs. Doesn't work for autoload nor manual loading with crane.
Because it is for short logs only...
As far as I know, there are no short logs in this game. Only medium and long.