We have an assert in wt_evict 

WT_ASSERT(session,
  closing || !F_ISSET(ref, WT_REF_FLAG_INTERNAL) ||
    F_ISSET(session->dhandle, WT_DHANDLE_DEAD) ||
    !__wt_gen_active(session, WT_GEN_SPLIT, page->pg_intl_split_gen)); 

That asserts that we don't evict an accessible internal page with an active split generation. Violating it means every child WT_REF is freed from under any thread still walking that index.

We have seen crashes where __wt_evict → an unmapped address. Checking this field may be able to diagnose whether a bad free caused the invalid address access. 

Convert the assert to use the existing eviction_check category:

WT_ASSERT_OPTIONAL(session, WT_DIAGNOSTIC_EVICTION_CHECK, <existing predicate>,
  "Evicting an accessible internal page with an active split generation"); 

So the check can be toggled on a release build via extra_diagnostics=[eviction_check].