Metal crash on iOS app start

We’re getting a random crash on game startup, 1/10 seconds after tapping the app icon; game crashes almost as soon as the app icon is tapped.
The crash log looks like this:

Exception Subtype: KERN_INVALID_ADDRESS at 0x0000000000000258
Triggered by Thread: 0

Thread 0 name: Dispatch queue:
Thread 0 Crashed:
0 AGXMetalG4P 0x00000001045fed28 0x1045f0000 + 60712
1 AGXMetalG4P 0x00000001045ffbb8 0x1045f0000 + 64440

Crash only happens when Graphics API is set to Automatic, does not happen with Open GL.
Crash happens infrequently, about once every 2 days, however players are reporting it happening very frequently in game too.
We contacted apple and they said it was something we’re doing. We don’t think our game code is running so early in the startup sequence, so we suspect Unity…

Has anyone else experienced this crash?
Does that crash dump look familiar to anyone else?
Can anyone recommend a fix or suggest a way to narrow down the issue?

Many thanks.

The latest 5.5.1 fixes the problem as I heard:

(857032) - Metal: Fixed a crash on startup on some iOS devices.