After an in-depth investigation, we have found a workaround: https://jira.unity3d.com/browse/BUR-1746?focusedCommentId=5371629&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-5371629
While we don't know the exact CPU instructions that cause the kernel panic, this workaround should unblock the customer, and we believe this particular issue is specific to the CPU used in iPad Mini 4. It's probably a hardware bug, triggered by a certain set of instructions (but not immediately, which is why when it crashes, it's not inside a Burst method). But without the ability to get a core at the point of failure, we cannot know for sure.