If log redaction is enabled, then WiredTiger errors also get redacted:
2019-02-04T13:05:59.336-0500 E STORAGE [thread3006] WiredTiger error (-31804) ###
This is how a sample message like that looks if not redacted:
2018-05-10T19:26:23.657+0100 E STORAGE [thread1] WiredTiger (-31804) [1525976783:657574][1:0x7f2e2279b700], file:mongoose_riskdev/index/475--5542394675829158327.wt, WT_SESSION.checkpoint: the process must exit and restart: WT_PANIC: WiredTiger library panic
As you can see, this message does not have any PII information and therefore the redaction is not justified.
This is a defect that makes diagnostics harder.