ok, the query looks ok and you say it does work.
Now, it's the question, why you don't get any output.
what happens, when you remove
the &tpl - property
what is the content of your chunk search.calender.list.item
I can't think, why migxLoopCollection doesn't output any results there.
It doesn't make much differently than what your snippet does, internally.
And the strange thing is, that it's working for me on my site.
yeah it really strange... I have absolutely no idea what it could be.
But I'm glad I got it working now another way, and I just hope to never run into this ever again ;-)
Thanks for all your help!