Why does unsafeBitCast crash while assumingMemoryBound works in my Swift Audio Unit callback?

I'm using the Apple Audio Unit v2 API in Swift and encountered a bug when working with an UnsafeMutableRawPointer in AURenderCallback. I built a toy example to isolate the issue, as shown below:

SWIFTCopied
import Foundation

class MyInfo {
  var i: Int = 3
}

class MyDelegate {
  var info: MyInfo?
}

func renderCallback(_ ref: UnsafeMutableRawPointer) {
  var d: MyDelegate = ref.assumingMemoryBound(to: MyDelegate.self).pointee
  // var d: MyDelegate = unsafeBitCast(ref, to: MyDelegate.self) // crash!
  guard var a = d.info else { return }
  a.i = 32
  print(d.info?.i)
}

var d = MyDelegate()
d.info = MyInfo()
renderCallback(&d) // in real application, this is called by audio toolbox framework
print(d.info?.i)

The code works correctly when using assumingMemoryBound, but crashes at runtime when I replace it with unsafeBitCast. Although the two approaches might seem equivalent, I'm trying to understand the core difference between them and why unsafeBitCast fails in this scenario.