The double quotes cause the function to ignore the forward slash.
Instead, $strchr is returning the position of the first white-space, because that is the character following the comma.
Try this: $trim($left(%comment%,$sub($strchr(%comment%,/),1)))
(I don't know what %d% is so I used %comment% for an example)
$left('Hans Christian / Any Title',$sub($strstr('Hans Christian / Any Title',' / '),1))==>'Hans Christian'... or using a tag-field ...$left(%TITLE%,$sub($strstr(%TITLE%,' / '),1))... or ...$regexp(%TITLE%,'^(.+?) / (.+?)$','$1')