its going to totally rely on whatever is in that $_items value. if you put a {debug} in that location and look at what $_items looks like that will tell you what the issue is.
the IN search parameter is expecting a comma separated list:
something,other,more
Thats not what I would expect to be in the $_items variable if it is what I think it is.
Might be that you need to change the structure of $_items to create a new variable to get done what your after.
If it was me, I'd first try with static content
{jrTags_cloud height="300" search="gallery_image_title in one for all,enter sandman"}
and see if thats what your after. If it is then figure out how to get that structure into a variable. Probably with 'explode'