>submitted a bug report
I think the latest tools are more chatty w/iOS 12.x. If you think those warnings are actionable, however, your best approach might be to burn a ticket w/DTS via the Member Center, being sure to have a buildable project of your store app they can take a look at.
I am seeing the same exact problem. My application makes use of MetalKit and AVAudioEngine for what it is worth. The leaks began showing up in the tools after 12.2. I can confirm that the same exact code running Leaks instrument will have zero leaks with iOS 12.1.2. Under 12.2 and 12.3 many of the core frameworks appear to be leaking. Appears that XCode 10.2 + iOS 12.2 or greater is an issue, noticed this thread: https://forums.developer.apple.com/thread/115120