Earlier this month, a report emerged of an Apple Music user who lost half of the files stored locally on their system. While the service isn't designed to function that way, it turns out an iTunes bug may have caused the deletion of files. Apple has since confirmed the issue, and said that it is working on a patch.
In a bid to understand the exact nature of the problem, Apple has sent out two engineers to the residence of the user that first reported the issue. From Vellum Atlanta:
Through an external drive connected to my laptop, we were now using a specialized version of iTunes in the hopes that the deletion would again occur; an idea that we knew may not pan out, since I'd had Apple Music for eight months before that first mass deletion. If something did go wrong, though, this version of iTunes would document what happened in more detail than the consumer version could.
We spent hours troubleshooting, but the problem eluded us. This time, the files remained, which was just one of many confounding elements of my whole saga. The problem wasn't cut-and-dry, therefore has proven difficult to replicate. For example, one of the many confusing things about the initial file loss was that only most of my music files had disappeared. Most, but not all.
While the engineers were not able to recreate the bug, Apple will be rolling out an update to iTunes that provides additional safeguards.