Hi there, which version of Logic do you use, could you specify? I remember someone posted a question with exactly the same issue as yours a few weeks ago. Not sure really if the person who asked it managed to find a solution. But having this in mind, if you're running a recent version, i.e. 10.7.3 or later, this might as well be a bug.
As a sort of a "home remedy", you could try reindexing all loops: in Loop browser, click on "Loop Packs" to display all available loop libraries, then choose "Reindex All Loops" at the bottom of this list. It takes a few minutes to complete, but not too long.
Please, report back if it doesn't fix the problem. We'll dig deeper. Cheers!