Huge Camera.Render spike on device, no information

I have an iOS game that will occasionally freeze, but only on the device, never in the editor. It’s not consistently reproducible, but almost always happens eventually - sometimes soon after launch. When I profile one of these crashes I see this:

There is a crazy spike in Camera.Render, but it is all in Self, so what is causing it? There are no accompanying error messages. This usually causes a crash for memory reasons, but not always - sometimes the game recovers.

What can I do to diagnose this problem?

Just for others who find the thread:
The problem was solved in the forum (https://forum.unity3d.com/threads/huge-camera-render-spike-on-ios-device.389821/ ). It was connected to ad banners.